Fix DirName() in case of relative path like "aap/". Fix ROOT-5026.
Fix DirName() in case of relative path like "aap/". Fix ROOT-5026.

Patch by Oliver Freyermuth and me.

Duraznos/root,zzxuanyuan/root,simonpf/root,zzxuanyuan/root,vukasinmilosevic/root,mkret2/root,georgtroska/root,beniz/root,vukasinmilosevic/root,satyarth934/root,jrtomps/root,dfunke/root,omazapa/root-old,esakellari/my_root_for_test,mhuwiler/rootauto,root-mirror/root,arch1tect0r/root,agarciamontoro/root,nilqed/root,BerserkerTroll/root,evgeny-boger/root,buuck/root,jrtomps/root,lgiommi/root,pspe/root,olifre/root,CristinaCristescu/root,pspe/root,thomaskeck/root,omazapa/root-old,root-mirror/root,0x0all/ROOT,root-mirror/root,mhuwiler/rootauto,cxx-hep/root-cern,lgiommi/root,beniz/root,root-mirror/root,satyarth934/root,olifre/root,sbinet/cxx-root,cxx-hep/root-cern,omazapa/root,Y--/root,gganis/root,davidlt/root,buuck/root,sirinath/root,arch1tect0r/root,vukasinmilosevic/root,jrtomps/root,gbitzes/root,davidlt/root,thomaskeck/root,cxx-hep/root-cern,root-mirror/root,krafczyk/root,sirinath/root,veprbl/root,CristinaCristescu/root,Y--/root,simonpf/root,omazapa/root-old,georgtroska/root,root-mirror/root,perovic/root,nilqed/root,karies/root,bbockelm/root,karies/root,esakellari/my_root_for_test,thomaskeck/root,sirinath/root,Duraznos/root,bbockelm/root,pspe/root,vukasinmilosevic/root,olifre/root,gganis/root,satyarth934/root,veprbl/root,cxx-hep/root-cern,0x0all/ROOT,cxx-hep/root-cern,gganis/root,buuck/root,Y--/root,mattkretz/root,omazapa/root,olifre/root,dfunke/root,satyarth934/root,arch1tect0r/root,omazapa/root,mattkretz/root,veprbl/root,BerserkerTroll/root,nilqed/root,mkret2/root,beniz/root,gganis/root,georgtroska/root,omazapa/root,evgeny-boger/root,simonpf/root,mhuwiler/rootauto,gbitzes/root,sbinet/cxx-root,mattkretz/root,cxx-hep/root-cern,karies/root,smarinac/root,dfunke/root,root-mirror/root,Y--/root,esakellari/my_root_for_test,arch1tect0r/root,sirinath/root,zzxuanyuan/root-compressor-dummy,zzxuanyuan/root-compressor-dummy,gbitzes/root,mhuwiler/rootauto,gganis/root,BerserkerTroll/root,olifre/root,evgeny-boger/root,karies/root,Y--/root,sbinet/cxx-root,jrtomps/root,omazapa/root-old,zzxuanyuan/root,georgtroska/root,alexschlueter/cern-root,simonpf/root,zzxuanyuan/root-compressor-dummy,Duraznos/root,gbitzes/root,sbinet/cxx-root,alexschlueter/cern-root,olifre/root,omazapa/root,karies/root,jrtomps/root,beniz/root,BerserkerTroll/root,cxx-hep/root-cern,omazapa/root,karies/root,buuck/root,arch1tect0r/root,zzxuanyuan/root-compressor-dummy,mattkretz/root,zzxuanyuan/root-compressor-dummy,gganis/root,davidlt/root,zzxuanyuan/root,sbinet/cxx-root,krafczyk/root,esakellari/root,dfunke/root,beniz/root,BerserkerTroll/root,omazapa/root-old,krafczyk/root,omazapa/root-old,zzxuanyuan/root,BerserkerTroll/root,buuck/root,lgiommi/root,mkret2/root,beniz/root,agarciamontoro/root,smarinac/root,agarciamontoro/root,Duraznos/root,sbinet/cxx-root,zzxuanyuan/root-compressor-dummy,omazapa/root-old,georgtroska/root,lgiommi/root,0x0all/ROOT,CristinaCristescu/root,pspe/root,BerserkerTroll/root,abhinavmoudgil95/root,esakellari/root,veprbl/root,lgiommi/root,esakellari/root,jrtomps/root,pspe/root,beniz/root,nilqed/root,omazapa/root-old,mkret2/root,thomaskeck/root,georgtroska/root,dfunke/root,esakellari/my_root_for_test,zzxuanyuan/root,mkret2/root,mkret2/root,zzxuanyuan/root,smarinac/root,abhinavmoudgil95/root,georgtroska/root,dfunke/root,zzxuanyuan/root,vukasinmilosevic/root,BerserkerTroll/root,mattkretz/root,sbinet/cxx-root,arch1tect0r/root,Duraznos/root,zzxuanyuan/root-compressor-dummy,BerserkerTroll/root,olifre/root,mattkretz/root,pspe/root,dfunke/root,dfunke/root,abhinavmoudgil95/root,jrtomps/root,smarinac/root,mhuwiler/rootauto,davidlt/root,satyarth934/root,mkret2/root,veprbl/root,gbitzes/root,mhuwiler/rootauto,perovic/root,zzxuanyuan/root-compressor-dummy,karies/root,evgeny-boger/root,CristinaCristescu/root,root-mirror/root,krafczyk/root,esakellari/my_root_for_test,sawenzel/root,nilqed/root,evgeny-boger/root,vukasinmilosevic/root,esakellari/root,agarciamontoro/root,simonpf/root,mhuwiler/rootauto,gganis/root,sirinath/root,0x0all/ROOT,simonpf/root,vukasinmilosevic/root,evgeny-boger/root,omazapa/root,sawenzel/root,pspe/root,krafczyk/root,lgiommi/root,BerserkerTroll/root,gganis/root,arch1tect0r/root,buuck/root,smarinac/root,zzxuanyuan/root,CristinaCristescu/root,0x0all/ROOT,agarciamontoro/root,bbockelm/root,veprbl/root,vukasinmilosevic/root,pspe/root,karies/root,perovic/root,bbockelm/root,buuck/root,gbitzes/root,gganis/root,krafczyk/root,sawenzel/root,sirinath/root,perovic/root,olifre/root,root-mirror/root,olifre/root,smarinac/root,esakellari/root,Y--/root,cxx-hep/root-cern,perovic/root,sbinet/cxx-root,alexschlueter/cern-root,CristinaCristescu/root,mattkretz/root,Duraznos/root,pspe/root,sawenzel/root,esakellari/root,CristinaCristescu/root,satyarth934/root,omazapa/root-old,thomaskeck/root,esakellari/my_root_for_test,beniz/root,evgeny-boger/root,CristinaCristescu/root,bbockelm/root,sirinath/root,CristinaCristescu/root,georgtroska/root,sirinath/root,olifre/root,Duraznos/root,satyarth934/root,bbockelm/root,davidlt/root,buuck/root,jrtomps/root,vukasinmilosevic/root,satyarth934/root,sbinet/cxx-root,jrtomps/root,georgtroska/root,mhuwiler/rootauto,nilqed/root,agarciamontoro/root,BerserkerTroll/root,Y--/root,arch1tect0r/root,davidlt/root,krafczyk/root,krafczyk/root,Y--/root,sawenzel/root,mattkretz/root,agarciamontoro/root,smarinac/root,smarinac/root,simonpf/root,nilqed/root,lgiommi/root,krafczyk/root,Duraznos/root,gbitzes/root,karies/root,bbockelm/root,alexschlueter/cern-root,esakellari/root,abhinavmoudgil95/root,sirinath/root,buuck/root,sirinath/root,buuck/root,abhinavmoudgil95/root,root-mirror/root,sbinet/cxx-root,gbitzes/root,evgeny-boger/root,omazapa/root,davidlt/root,Y--/root,dfunke/root,veprbl/root,mhuwiler/rootauto,sawenzel/root,bbockelm/root,davidlt/root,gbitzes/root,omazapa/root-old,esakellari/my_root_for_test,omazapa/root,perovic/root,sawenzel/root,0x0all/ROOT,zzxuanyuan/root-compressor-dummy,thomaskeck/root,agarciamontoro/root,pspe/root,karies/root,mattkretz/root,evgeny-boger/root,veprbl/root,mhuwiler/rootauto,agarciamontoro/root,esakellari/my_root_for_test,alexschlueter/cern-root,simonpf/root,0x0all/ROOT,karies/root,omazapa/root,jrtomps/root,bbockelm/root,mkret2/root,mkret2/root,thomaskeck/root,nilqed/root,buuck/root,veprbl/root,gbitzes/root,smarinac/root,esakellari/root,sawenzel/root,zzxuanyuan/root,dfunke/root,root-mirror/root,esakellari/root,veprbl/root,zzxuanyuan/root-compressor-dummy,pspe/root,mhuwiler/rootauto,simonpf/root,nilqed/root,evgeny-boger/root,arch1tect0r/root,smarinac/root,nilqed/root,agarciamontoro/root,krafczyk/root,jrtomps/root,sawenzel/root,esakellari/my_root_for_test,gbitzes/root,simonpf/root,lgiommi/root,omazapa/root-old,arch1tect0r/root,nilqed/root,esakellari/my_root_for_test,abhinavmoudgil95/root,zzxuanyuan/root-compressor-dummy,dfunke/root,sirinath/root,abhinavmoudgil95/root,sawenzel/root,georgtroska/root,satyarth934/root,lgiommi/root,simonpf/root,zzxuanyuan/root,agarciamontoro/root,alexschlueter/cern-root,thomaskeck/root,olifre/root,arch1tect0r/root,zzxuanyuan/root,perovic/root,evgeny-boger/root,satyarth934/root,gganis/root,thomaskeck/root,davidlt/root,beniz/root,abhinavmoudgil95/root,perovic/root,veprbl/root,gganis/root,abhinavmoudgil95/root,CristinaCristescu/root,Y--/root,alexschlueter/cern-root,lgiommi/root,abhinavmoudgil95/root,Duraznos/root,vukasinmilosevic/root,perovic/root,perovic/root,omazapa/root,davidlt/root,krafczyk/root,mkret2/root,0x0all/ROOT,satyarth934/root,mattkretz/root,mkret2/root,Duraznos/root,CristinaCristescu/root,Duraznos/root,mattkretz/root,beniz/root,beniz/root,davidlt/root,sbinet/cxx-root,vukasinmilosevic/root,sawenzel/root,bbockelm/root,0x0all/ROOT,thomaskeck/root,esakellari/root,esakellari/root,abhinavmoudgil95/root,georgtroska/root,Y--/root,perovic/root,bbockelm/root,lgiommi/root