Report error on duplicate constructor or destructor in class
Report error on duplicate constructor or destructor in class

Fixes bug 600581.

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