[impdev] 1.3.1 bugfix version

[Jacek Antonelli]

Armin has proposed we release a new version in the 1.3 series, to
support the increased group limit in SL (you can now join up to 42
groups). That sounds good to me, plus I have been wanting to release a
version 1.3.1 with some important bug fixes (like IMP-629, snapshot
freeze-frame messing up mouse input).

My 1.3-maint branch has the code for 1.3.1 so far:

  https://github.com/jacek/imprudence/commits/1.3-maint

Are there any other important bug fixes or changes that should go into 1.3.1?

- Jacek