heptapod-ci: add a script to map evolve branch to mercurial revision for tests map-hg-rev.sh can be tested using this command: ```sh for i in $(hg log -T '{branch}\n' | sort -u); do echo $i $(testlib/map-hg-rev.sh $i) done ```

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. $TESTDIR/testlib/pythonpath.sh

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cat >> $HGRCPATH << EOF

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[extensions]

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docgraph=

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EOF