Primary selection pasting to (some) gtk apps.

[Vladimir-csp]

Can't do it on 0.48.1 (and it was that way all the way back to 0.40). I.e. Firefox or Geany do not receive anything on middle click. But Chromium and Papers do. The source of selection doesn't seem to matter.

Poked these with middle click:

Works: featherpad_wldebug.log
Works: chromium_wldebug.log
Does not: geany_wldebug.log