readline: various fixes to delegates and attributes
readline: various fixes to delegates and attributes

It's now possible to do readline completion.

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