Seahorse and GTK+3

[Stef Walter <stefw gnome org>]

I worked on a bunch of migrations and testing with GTK+ 3.0 today. A
bunch of #ifdefs and autotools-fidgeting later and:

 seahorse
   - Now works with GTK+ 3.0
   - Now using libgck from gnome-keyring.
   - No parallel install of anything since libcryptui is going away.
   - Will release 2.91.1 shortly.

 seahorse-plugins
   - Now works with GTK+ 3.0
   - Need someone to do release, since it doesn't distcheck for me.
     Can't figure out the mozilla/epiphany stuff.

 gnome-keyring
   - New ui-widgets stuff builds with GTK+ 3.0
   - Fixed broken install of libgck.
   - A while back, Phillip worked on parallel install of libgcr
     gnome-keyring (tool) and other bits.
   - Will release 2.91.1 shortly.

All of the above is in master of each project. Use --with-gtk=3.0 to
enable building against GTK3.

I'm pretty braindead after all this, so I'll wait a day before
releasing, in case anyone notices anything strange and broken.

Cheers,

Stef