Removing test_plugins_index

This test seems unnecessary now, since after every change we have
to generate plugins_index.txt and manually check to ensure it is
correct.
Improvements in plugins_index.txt

- Removed author and email in favor of repository link.
  Repository link is obtained from the 'home_page' field
  obtained from pypi. For plugins that don't have
  that field set, function obtain_override_repositories
  is used to override it in favor of known repositories url.

- Shortened "Python 2.7" in favor of "py27" to save space;
  Same for "Python 3.3".
Updated plugins_index.txt after changes in plugin_index.py
plugins_index: status images now link to actual tox output
trim trailing spaces
replace py.test module references with pytest

The only remaining 'py.test' references are:
 * those referring to the 'py.test' executable
 * those in code explicitly testing py.test/pytest module compatibility
 * those in old CHANGES documentation
 * those in documentation generated based on external data
 * those in seemingly unfinished & unmaintained Japanese documentation

Minor stylistic changes and typo corrections made to documentation next to
several applied py.test --> pytest content changes.
fix comment typos
update README.rst docs - pytest is compatible with Python 2.5 instead of 2.4
Merged in jurko/pytest (pull request #100)

update README.rst docs - pytest is compatible with Python 2.5 instead of 2.4
added changelog: fixed docs and code to use "pytest" instead of "py.test"
everywhere.  Thanks Jurko Gspodnetic for the complete PR.