Fix relational operations involving nullable types
Fix relational operations involving nullable types

Fixes bug 600652.

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