Fix i18n support by adding back ENABLE_NLS.

https://bugzilla.gnome.org/show_bug.cgi?id=727501
Bug 732155 - Fix initializing Python loader from Python application

https://bugzilla.gnome.org/show_bug.cgi?id=732155
Prevent and warn when trying to enable multiple loaders

Using multiple plugin loaders will cause memory leaks due to
both the python 2/3 and seed binding using toggle refs. Also
mixing python version will never work.
Chain-up to finalize in the python plugin loader
Simplify installing gettext in the python plugin loader

Also check for an error after installing.
Don't print the exception if a python module failed to import

The PeasPluginInfo will have an error of "Failed to load".
Remove INSTALL file
Fix error message when popping log hooks fails
TEMP ---*DO NO COMMIT*--- TEMP
Have silent subprocess tests inherit stderr for easier debugging

For the engine shutdown test we cannot inherit stderr as it
prints to stderr.
Be more explicit about when a plugin loader is not enabled

Also silence a warning when we have already warned.
Do not test the properties for Python extensions

Because Python extensions are no longer wrapped testing
the properties is just pointless.
Bug 678338 - Check return values from Python API

https://bugzilla.gnome.org/show_bug.cgi?id=678338
Add easy python profiling support

When the PEAS_PYTHON_PROFILE enviroment variable
is set profiling information will be output when all python
plugins are unloaded.