Do not allow assigning to construct-only properties of foreign objects
Do not allow assigning to construct-only properties of foreign objects

Fixes bug 604590.

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