girparser: Update to prefix handling used in GIR version 1.2
girparser: Update to prefix handling used in GIR version 1.2

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