gnome-keyring no longer sets a GNOME_KEYRING_CONTROL
environment variable.

It has used DBus for years now, and this was an old vestige
of the previous ancient protocol.

See: https://bugzilla.gnome.org/show_bug.cgi?id=725801

https://mail.gnome.org/archives/gnome-keyring-list/2014-March/msg00000.html
Update changelog
Use Python 2.6 syntax for exception handler
Add a compatibility layer for older versions of Pywin32. Fixes #140.