vapigen: Improve support for type_arguments
vapigen: Improve support for type_arguments

Fixes bug 609693.

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