buildbot/buildbot — pull request #363 by sdegrande (2012-03-16 17:59:56+00:00)
Title: FETCH_HEAD is not used when force-building without defining a revision.

When force-building is used on the WebStatus page on a specific branch
but without defining a specific revision, the current master HEAD is used
instead of the branch HEAD.
That's due to the ForceSheduler using a empty string as the default value
for a revision, while the git _fetch() expecting a NULL value to use FETCH_BRANCH.
This patch add a test against the empty string in git _fetch().