gidlparser: Support hiding interfaces with metadata
gidlparser: Support hiding interfaces with metadata

Fixes bug 627298.

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