Report error when trying to use signals as expressions
Report error when trying to use signals as expressions

Fixes bug 437431.

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