Support set accessors in internal VAPI properties
Support set accessors in internal VAPI properties

Fixes bug 545187.

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