Report error when signal exists more than once in type hierarchy
Report error when signal exists more than once in type hierarchy

tjol/vala-tjol,playya/vala,frida/vala,themiwi/vala,playya/vala,spidermonkdust/vala,kamanashisroy/aroop,flobrosch/vala-fixes,severinh/vala,kamanashisroy/aroop,rvu95/vala,xdave/pvala,Distrotech/vala,tjol/vala-tjol,playya/vala,frida/vala,Distrotech/vala,lovebug356/vala,rvu95/vala,flobrosch/vala-fixes,spidermonkdust/vala,phako/vala,Distrotech/vala,severinh/vala,tjol/vala-tjol,rvu95/vala,Jc2k/vala,jessevdk/vala,lovebug356/vala,phako/vala,frida/vala,GNOME/vala,themiwi/vala,Jc2k/vala,themiwi/vala,frida/vala,severinh/vala,jessevdk/vala,frida/vala,GNOME/vala,flobrosch/vala-fixes,GNOME/vala,spidermonkdust/vala,jessevdk/vala,kamanashisroy/aroop,GNOME/vala