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--
extra : rebase_source : 642634a4005cf1261e99825c97a6e5c82b069183
debuginstall: change showing to checking for consistency and future checking

--HG--
extra : rebase_source : 6fcd39764879295058900fb00f71000e2e3726a5
parsers: fail fast if Python has wrong minor version (issue4110)

This change causes an informative ImportError to be raised when importing
the parsers extension module if the minor version of the currently-running
Python interpreter doesn't match that of the Python used when compiling
the extension module.

This change also exposes a parsers.versionerrortext constant in the
C implementation of the module.  Its presence can be used to determine
whether this behavior is present in a version of the module.  The value
of the constant is the leading text of the ImportError raised and is set
to "Python minor version mismatch".

Here is an example of what the new error looks like:

  Traceback (most recent call last):
    File "test.py", line 1, in <module>
      import mercurial.parsers
  ImportError: Python minor version mismatch: The Mercurial extension
  modules were compiled with Python 2.7.6, but Mercurial is currently using
  Python with sys.hexversion=33883888: Python 2.5.6
  (r256:88840, Nov 18 2012, 05:37:10)
  [GCC 4.2.1 Compatible Apple Clang 4.1 ((tags/Apple/clang-421.11.66))]
   at: /opt/local/Library/Frameworks/Python.framework/Versions/2.5/Resources/
    Python.app/Contents/MacOS/Python

The reason for raising an error in this scenario is that Python's C API
is known not to be compatible from minor version to minor version, even
if sys.api_version is the same.  See for example this Python bug report
about incompatibilities between 2.5 and 2.6+:

  http://bugs.python.org/issue8118

These incompatibilities can cause Mercurial to break in mysterious,
unforeseen ways.  For example, when Mercurial compiled with Python 2.7 was
run with 2.5, the following crash occurred when running "hg status":

  http://bz.selenic.com/show_bug.cgi?id=4110

After this crash was fixed, running with Python 2.5 no longer crashes, but
the following puzzling behavior still occurs:

    $ hg status
      ...
      File ".../mercurial/changelog.py", line 123, in __init__
        revlog.revlog.__init__(self, opener, "00changelog.i")
      File ".../mercurial/revlog.py", line 251, in __init__
        d = self._io.parseindex(i, self._inline)
      File ".../mercurial/revlog.py", line 158, in parseindex
        index, cache = parsers.parse_index2(data, inline)
    TypeError: data is not a string

which can be reproduced more simply with:

    import mercurial.parsers as parsers
    parsers.parse_index2("", True)

Both the crash and the TypeError occurred because the Python C API's
PyString_Check() returns the wrong value when the C header files from
Python 2.7 are run with Python 2.5.  This is an example of an
incompatibility of the sort mentioned in the Python bug report above.

Failing fast with an informative error message results in a better user
experience in cases like the above.  The information in the ImportError
also simplifies troubleshooting for those on Mercurial mailing lists, the
bug tracker, etc.

This patch only adds the version check to parsers.c, which is sufficient
to affect command-line commands like "hg status" and "hg summary".
An idea for a future improvement is to move the version-checking C code
to a more central location, and have it run when importing all
Mercurial extension modules and not just parsers.c.

--HG--
extra : rebase_source : 4b1bcd5c4c3e7f7449dc11291bf6a29607cccc30
help: filter out deprecated options with untranslated descriptions

When using a different language than English, deprecated options were only
removed from the output of `hg help anycmd` when "DEPRECATED" in the options
description was translated.

--HG--
extra : rebase_source : 74a2288b33ca7a5de24f10a2d1e33c9eecf26ac9