Make marked merge base invalid when the upstream changes.

Make marked merge base invalid when the upstream changes.

This should let the base marker transparently work with plain-old-git tools
which was the idea in the first place. Specifically `git branch -u` without a
corresponding rebase.

R=agable@chromium.org
BUG=373977
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=271112

[iannucci, 2014-05-15 22:20:17]

https://codereview.chromium.org/288323002/diff/1/git_map.py
File git_map.py (right):

https://codereview.chromium.org/288323002/diff/1/git_map.py#newcode53
git_map.py:53: merge_base_map = {b: v for b, v in merge_base_map.iteritems() if
v}
this fixes a bug for branches which have NO upstream defined.

https://codereview.chromium.org/288323002/diff/1/git_reparent_branch.py
File git_reparent_branch.py (right):

https://codereview.chromium.org/288323002/diff/1/git_reparent_branch.py#newco...
git_reparent_branch.py:69: manual_merge_base(branch, mbase, new_parent)
this sets the same base for the branch given the new parent branch.

https://codereview.chromium.org/288323002/diff/1/tests/git_common_test.py
File tests/git_common_test.py (right):

https://codereview.chromium.org/288323002/diff/1/tests/git_common_test.py#new...
tests/git_common_test.py:402: self.assertIn('too many branches (39/20)', rslt)
these were printing output during the test execution, so changed to
'capture_stdio'

[agable, 2014-05-16 21:59:08]

LGTM

[iannucci, 2014-05-16 22:19:44]

The CQ bit was checked by iannucci@chromium.org

[iannucci, 2014-05-16 22:31:17]

Committed patchset #1 manually as r271112 (presubmit successful).