Report error on duplicate switch label
Report error on duplicate switch label

Fixes bug 572556.

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