Override CleanAllProjects instead of Clean in build.proj
Override CleanAllProjects instead of Clean in build.proj

Prior to this change, build.proj overrode the Clean target
directly which did not honor TraversalCleanDependsOn.  This
meant other repo's could not customize the behavior of
a clean, either via Clean.cmd or 'build /t:clean'.

With this change, other repo's can add custom build targets
to TraversalCleanDependsOn to do pre- or post- clean handling.
WCF in particular requires this.

jhendrixMSFT/corefx,nbarbettini/corefx,shmao/corefx,shimingsg/corefx,rahku/corefx,wtgodbe/corefx,Petermarcu/corefx,the-dwyer/corefx,stephenmichaelf/corefx,tijoytom/corefx,Jiayili1/corefx,dhoehna/corefx,rubo/corefx,parjong/corefx,manu-silicon/corefx,zhenlan/corefx,gkhanna79/corefx,stone-li/corefx,elijah6/corefx,the-dwyer/corefx,stone-li/corefx,Ermiar/corefx,twsouthwick/corefx,marksmeltzer/corefx,twsouthwick/corefx,Priya91/corefx-1,Priya91/corefx-1,gkhanna79/corefx,gkhanna79/corefx,marksmeltzer/corefx,shimingsg/corefx,cydhaselton/corefx,marksmeltzer/corefx,shmao/corefx,iamjasonp/corefx,DnlHarvey/corefx,khdang/corefx,parjong/corefx,ptoonen/corefx,Petermarcu/corefx,axelheer/corefx,billwert/corefx,Jiayili1/corefx,dotnet-bot/corefx,lggomez/corefx,tijoytom/corefx,elijah6/corefx,nchikanov/corefx,ravimeda/corefx,shimingsg/corefx,zhenlan/corefx,tijoytom/corefx,gkhanna79/corefx,dotnet-bot/corefx,rjxby/corefx,dhoehna/corefx,nchikanov/corefx,shimingsg/corefx,DnlHarvey/corefx,dotnet-bot/corefx,YoupHulsebos/corefx,seanshpark/corefx,twsouthwick/corefx,krytarowski/corefx,the-dwyer/corefx,cydhaselton/corefx,rubo/corefx,seanshpark/corefx,yizhang82/corefx,ellismg/corefx,ptoonen/corefx,axelheer/corefx,Ermiar/corefx,ellismg/corefx,rjxby/corefx,billwert/corefx,elijah6/corefx,stone-li/corefx,dsplaisted/corefx,Jiayili1/corefx,stephenmichaelf/corefx,manu-silicon/corefx,cydhaselton/corefx,weltkante/corefx,fgreinacher/corefx,rjxby/corefx,manu-silicon/corefx,weltkante/corefx,khdang/corefx,wtgodbe/corefx,alexperovich/corefx,Jiayili1/corefx,JosephTremoulet/corefx,yizhang82/corefx,ViktorHofer/corefx,weltkante/corefx,nchikanov/corefx,cydhaselton/corefx,Priya91/corefx-1,dotnet-bot/corefx,ptoonen/corefx,dhoehna/corefx,alphonsekurian/corefx,khdang/corefx,JosephTremoulet/corefx,jhendrixMSFT/corefx,dhoehna/corefx,the-dwyer/corefx,twsouthwick/corefx,ravimeda/corefx,ericstj/corefx,rubo/corefx,nchikanov/corefx,nchikanov/corefx,jlin177/corefx,Jiayili1/corefx,dotnet-bot/corefx,alphonsekurian/corefx,alphonsekurian/corefx,MaggieTsang/corefx,ravimeda/corefx,parjong/corefx,mmitche/corefx,JosephTremoulet/corefx,twsouthwick/corefx,stone-li/corefx,marksmeltzer/corefx,jlin177/corefx,wtgodbe/corefx,ericstj/corefx,mmitche/corefx,shmao/corefx,shmao/corefx,YoupHulsebos/corefx,iamjasonp/corefx,billwert/corefx,Chrisboh/corefx,JosephTremoulet/corefx,billwert/corefx,zhenlan/corefx,JosephTremoulet/corefx,gkhanna79/corefx,jlin177/corefx,rjxby/corefx,mazong1123/corefx,rahku/corefx,richlander/corefx,ericstj/corefx,YoupHulsebos/corefx,cydhaselton/corefx,ptoonen/corefx,ericstj/corefx,rjxby/corefx,jlin177/corefx,stephenmichaelf/corefx,ravimeda/corefx,krk/corefx,stephenmichaelf/corefx,axelheer/corefx,twsouthwick/corefx,ericstj/corefx,MaggieTsang/corefx,manu-silicon/corefx,lggomez/corefx,seanshpark/corefx,krytarowski/corefx,manu-silicon/corefx,stone-li/corefx,mmitche/corefx,JosephTremoulet/corefx,cydhaselton/corefx,shmao/corefx,Chrisboh/corefx,Petermarcu/corefx,yizhang82/corefx,fgreinacher/corefx,zhenlan/corefx,zhenlan/corefx,adamralph/corefx,billwert/corefx,ravimeda/corefx,tijoytom/corefx,nchikanov/corefx,Petermarcu/corefx,Petermarcu/corefx,YoupHulsebos/corefx,rahku/corefx,Ermiar/corefx,krytarowski/corefx,dhoehna/corefx,marksmeltzer/corefx,manu-silicon/corefx,tijoytom/corefx,jhendrixMSFT/corefx,Jiayili1/corefx,rahku/corefx,MaggieTsang/corefx,nbarbettini/corefx,alexperovich/corefx,mazong1123/corefx,dotnet-bot/corefx,alexperovich/corefx,BrennanConroy/corefx,jlin177/corefx,Chrisboh/corefx,seanshpark/corefx,the-dwyer/corefx,MaggieTsang/corefx,ravimeda/corefx,parjong/corefx,MaggieTsang/corefx,krk/corefx,axelheer/corefx,jlin177/corefx,DnlHarvey/corefx,the-dwyer/corefx,gkhanna79/corefx,dotnet-bot/corefx,shimingsg/corefx,iamjasonp/corefx,rjxby/corefx,richlander/corefx,jhendrixMSFT/corefx,parjong/corefx,krytarowski/corefx,khdang/corefx,lggomez/corefx,ViktorHofer/corefx,twsouthwick/corefx,gkhanna79/corefx,marksmeltzer/corefx,Jiayili1/corefx,ravimeda/corefx,rubo/corefx,ellismg/corefx,stone-li/corefx,parjong/corefx,alphonsekurian/corefx,krytarowski/corefx,rjxby/corefx,dhoehna/corefx,mmitche/corefx,MaggieTsang/corefx,richlander/corefx,Priya91/corefx-1,richlander/corefx,Chrisboh/corefx,tijoytom/corefx,yizhang82/corefx,DnlHarvey/corefx,alexperovich/corefx,jhendrixMSFT/corefx,ellismg/corefx,adamralph/corefx,fgreinacher/corefx,shimingsg/corefx,rahku/corefx,axelheer/corefx,axelheer/corefx,Priya91/corefx-1,parjong/corefx,nbarbettini/corefx,ptoonen/corefx,rahku/corefx,khdang/corefx,richlander/corefx,krk/corefx,krytarowski/corefx,Ermiar/corefx,ericstj/corefx,mazong1123/corefx,nbarbettini/corefx,weltkante/corefx,DnlHarvey/corefx,stephenmichaelf/corefx,dhoehna/corefx,manu-silicon/corefx,seanshpark/corefx,BrennanConroy/corefx,Chrisboh/corefx,lggomez/corefx,nchikanov/corefx,ptoonen/corefx,ellismg/corefx,dsplaisted/corefx,DnlHarvey/corefx,YoupHulsebos/corefx,seanshpark/corefx,Ermiar/corefx,elijah6/corefx,jhendrixMSFT/corefx,alexperovich/corefx,iamjasonp/corefx,yizhang82/corefx,BrennanConroy/corefx,alexperovich/corefx,lggomez/corefx,iamjasonp/corefx,shimingsg/corefx,wtgodbe/corefx,seanshpark/corefx,alexperovich/corefx,billwert/corefx,Petermarcu/corefx,Ermiar/corefx,YoupHulsebos/corefx,billwert/corefx,fgreinacher/corefx,ericstj/corefx,alphonsekurian/corefx,jhendrixMSFT/corefx,elijah6/corefx,weltkante/corefx,weltkante/corefx,nbarbettini/corefx,krk/corefx,zhenlan/corefx,iamjasonp/corefx,lggomez/corefx,Petermarcu/corefx,zhenlan/corefx,stephenmichaelf/corefx,ViktorHofer/corefx,jlin177/corefx,adamralph/corefx,yizhang82/corefx,shmao/corefx,wtgodbe/corefx,mazong1123/corefx,richlander/corefx,Priya91/corefx-1,wtgodbe/corefx,Ermiar/corefx,rubo/corefx,stone-li/corefx,richlander/corefx,ViktorHofer/corefx,tijoytom/corefx,cydhaselton/corefx,ptoonen/corefx,krk/corefx,Chrisboh/corefx,JosephTremoulet/corefx,stephenmichaelf/corefx,krk/corefx,nbarbettini/corefx,krk/corefx,rahku/corefx,mmitche/corefx,the-dwyer/corefx,shmao/corefx,krytarowski/corefx,YoupHulsebos/corefx,ViktorHofer/corefx,ViktorHofer/corefx,alphonsekurian/corefx,alphonsekurian/corefx,weltkante/corefx,yizhang82/corefx,elijah6/corefx,wtgodbe/corefx,mazong1123/corefx,dsplaisted/corefx,nbarbettini/corefx,mazong1123/corefx,mmitche/corefx,khdang/corefx,DnlHarvey/corefx,MaggieTsang/corefx,lggomez/corefx,iamjasonp/corefx,elijah6/corefx,mmitche/corefx,ellismg/corefx,mazong1123/corefx,ViktorHofer/corefx,marksmeltzer/corefx