pgsql: Rename git_topo_order -> git_changelog, per discussion.

Rename git_topo_order -> git_changelog, per discussion.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=ce1dcd468f8a728398424296165a8d87eb36f0d8

Modified Files
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src/tools/RELEASE_CHANGES | 6 +-
src/tools/git_changelog | 161 +++++++++++++++++++++++++++++++++++++++++++++
src/tools/git_topo_order | 155 -------------------------------------------
3 files changed, 164 insertions(+), 158 deletions(-)