tests/test-diff-subdir.t

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.

  $ hg init

  $ mkdir alpha
  $ touch alpha/one
  $ mkdir beta
  $ touch beta/two

  $ hg add alpha/one beta/two
  $ hg ci -m "start"

  $ echo 1 > alpha/one
  $ echo 2 > beta/two

everything

  $ hg diff --nodates
  diff -r 7d5ef1aea329 alpha/one
  --- a/alpha/one
  +++ b/alpha/one
  @@ -0,0 +1,1 @@
  +1
  diff -r 7d5ef1aea329 beta/two
  --- a/beta/two
  +++ b/beta/two
  @@ -0,0 +1,1 @@
  +2

beta only

  $ hg diff --nodates beta
  diff -r 7d5ef1aea329 beta/two
  --- a/beta/two
  +++ b/beta/two
  @@ -0,0 +1,1 @@
  +2

inside beta

  $ cd beta
  $ hg diff --nodates .
  diff -r 7d5ef1aea329 beta/two
  --- a/beta/two
  +++ b/beta/two
  @@ -0,0 +1,1 @@
  +2

  $ cd ..