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.