packaging: introduce Python3 support as buildrpm --python3 Just overrule the HGPYTHON3 warning.

packaging: be explicit about Python version in rpm spec Fedora 31 has Python3 at /usr/bin/python ... but expect everybody to not just find python in $PATH but be explicit about whether they want python2 or python3. mercurial.spec just used 'python' and would fail when it unknowingly used Python 3 and ended up with Mercurial setup.py reporting "Python 3.7 detected." and talking about the HGPYTHON3 environment variable. For now, just be explicit about using system python2 as python executable when building rpms.

packaging: make python snippets in rpm building python3 compatible Fedora 31 has Python3 at /usr/bin/python, and buildrpm would fail on snippets that use python2 syntax. Instead of forcing python2, just accept for the future while staying backwards compatible.

py3: fix patchbomb to accept non-ASCII header value for email preview Since mail.headencode() is disabled by -n/--test, non-ASCII header value has to be allowed. Spotted by Denis Laxalde.

tests: check patchbomb with a non-ascii commit message This fails on Python 3 but gets fixed in the next changeset.

formatter: fix handling of None value in templater mapping For historical reasons, None in mapping dict means there's no such keyword, and falls back to b"". That's fine in log templates where mapping item is generally a callable returning a value (which may be None,) but the formatter directly puts an "evaluated" value in the mapping. So the None value has to be lifted to wrappedvalue(None) to avoid confusion in the template engine.

config: add support for defaultvalue of list of printable elements