Fixed #5494, #10765, #14924 -- Modified the order in which translations are read when composing the final translation to offer at runtime.

This is slightly backward-incompatible (could result in changed final translations for literals appearing multiple times in different .po files but with different translations).

Translations are now read in the following order (from lower to higher priority):

For the 'django' gettext domain:

 * Django translations
 * INSTALLED_APPS apps translations (with the ones listed first having higher priority)
 * settings/project path translations (deprecated, see below)
 * LOCALE_PATHS translations (with the ones listed first having higher priority)

For the 'djangojs' gettext domain:

 * Python modules whose names are passed to the javascript_catalog view
 * LOCALE_PATHS translations (with the ones listed first having higher priority, previously they weren't included)

Also, automatic loading of translations from the 'locale' subdir of the settings/project path is now deprecated.

Thanks to vanschelven, vbmendes and an anonymous user for reporting issues, to vanschelven, Claude Paroz and an anonymous contributor for their initial work on fixes and to Jannis  Leidel and Claude for review and discussion.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15441 bcc190cf-cafb-0310-a4f2-bffc1f526a37