t/Makefile: add a "prove" target

This makes it easy to run the tests using "prove" and allows setting
custom options for it in config.mak.

Signed-off-by: John Keeping <john@keeping.me.uk>
Pass --no-log to git-merge explicitly

If a user has configured "merge.log" then git-merge will add the log to
the commit message, on top of the one added by git-integration.  Pass
--no-log explicitly in order to override this behaviour.

Signed-off-by: John Keeping <john@keeping.me.uk>
Merge branch 't-prove-target'

* t-prove-target:
  t/Makefile: add a "prove" target
Merge branch 'pass-no-log-to-merge'

Avoid including the log twice in the integration merge messages if the
user has configured merge.log for their repository.

* pass-no-log-to-merge:
  Pass --no-log to git-merge explicitly