packaging: follow hg's supported python version (>= 2.7) "Mercurial 4.3 and newer require Python 2.7." (From https://www.mercurial-scm.org/wiki/SupportedPythonVersions) Also add X- prefix, because that's the correct form, apparently. This line can also be removed in future, since "When Debian supported multiple Python versions, X-Python-Version was used, but it is obsolete now as no supported Debian release supports anything other than python2.7." (From https://wiki.debian.org/Python/LibraryStyleGuide) That page also mentions "X-Python3-Version".

#require test-repo pyflakes

Copied from Mercurial core (60ee2593a270)

  $ cd "`dirname "$TESTDIR"`"

run pyflakes on all tracked files ending in .py or without a file ending
(skipping binary file random-seed)

  $ hg locate -I 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
  > | xargs pyflakes 2>/dev/null