debuginstall: add Python information to debuginstall output (issue4128) This change adds to the output of "hg debuginstall" information about the Python being used by Mercurial. It adds both the path to the Python executable (i.e. the value of sys.executable) and the version of Python (specifically the major, minor, and micro versions). Below is an example of what the output looks like after this change. The marked lines are the new output lines: $ hg debuginstall checking encoding (UTF-8)... -->showing Python executable (/Users/chris/.virtualenvs/default/bin/python) -->showing Python version (2.7.6) checking Python lib (/Users/chris/.virtualenvs/default/lib/python2.7)... checking installed modules (/Users/chris/mercurial)... checking templates (/Users/chris/mercurial/templates)... checking commit editor... checking username... no problems detected Note that we use the word "showing" without an ellipsis for the new lines because, unlike the other lines (except for "Python lib" which will be adjusted in a subsequent commit), no check follows the display of this information.