pgsql: Fix some more bugs in git_changelog.

Fix some more bugs in git_changelog.

1. Don't forget the last (oldest) commit on the oldest branch.

2. When considering which commit to print next, if two alternatives have
the same "distortion" score (which is actually the normal case, since
generally the "distortion" is 0), then choose the later timestamp to
print first. I don't know where Robert got the idea to ignore timestamps
and sort by branch age, but it wasn't a good idea: the resulting ordering
of commits was just plain bizarre anywhere that some branches had many
fewer commits than others, which is the typical situation for us.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=30d2e1005838c7ece353ef2ac269cfdc37e937be

Modified Files
--------------
src/tools/git_changelog | 37 +++++++++++++++++++------------------
1 files changed, 19 insertions(+), 18 deletions(-)