Reviewed by Adam Barth.

https://bugs.webkit.org/show_bug.cgi?id=35828

Keeping webkitpy/__init__.py free of non-trivial code allows
calling code to import initialization code from webkitpy
before any errors or log messages occur due to code in
__init__.py.  Such initialization code can include things like
version checking code and logging configuration code.  This
also lets us move the autoinstall initialization code to a
location where it only executes if it is needed -- something
we have done in this patch.

* Scripts/webkitpy/__init__.py:
  - Moved all executable code to the following location:
    webkitpy/thirdparty/autoinstalled/__init__.py
  - Added a code comment to keep this file free of non-trivial
    code.

* Scripts/webkitpy/bugzilla.py:
  - Updated mechanize import statement.

* Scripts/webkitpy/networktransaction.py:
  - Updated mechanize import statement.

* Scripts/webkitpy/networktransaction_unittest.py:
  - Updated mechanize import statement.

* Scripts/webkitpy/statusserver.py:
  - Updated mechanize import statement.

* Scripts/webkitpy/thirdparty/autoinstalled/__init__.py: Added.
  - Copied the code from webkitpy/__init__.py and updated it
    as necessary.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@55969 268f45cc-cd09-0410-ab3c-d52691b4dbfc