Patch for GBinding crash

[Matthew Barnes <mbarnes redhat com>]

Could I get someone to review an aging patch in:

https://bugzilla.gnome.org/show_bug.cgi?id=639873
"GBinding: Crash when binding two properties on the same instance"

I keep forgetting this still isn't fixed and so I have to continually
work around it.  Would be really nice to have it included in GLib 2.32.

Reproducer program is included in the bug.

Thanks,
Matthew Barnes