BUG Issue with login form failing to login in certain situations. Fixes issue #2424
Updating unit and integration testing documentation.

Updating introduction summary, and fixing broken links.
FAQ docs about composer install vs. archives

See http://www.silverstripe.org/installing-silverstripe/show/21447?start=8#post324638
Renamed "ja_JP" locale to "ja"

Better compat with transifex with generic locale
Merge branch 'refs/heads/3.1.0' into 3.1
Updated translations
Merge branch 'refs/heads/3.1.0' into 3.1
Corrected translation references in templates

Were using old entity naming scheme (*.ss) instead
of underscored version which doesn't create a new YML
namespace. This means all existing translations should indeed be used.
Was already fixed in master, but not in 3.1
More mappings for i18n::tinymce_lang
Behat test for language switching
Updated translations
Added 3.1.1 changelog
Merge pull request #2500 from halkyon/doc_updates

Updating unit and integration testing documentation.
Updated translations
Added 3.1.1 changelog
Merge remote-tracking branch 'origin/tmp-3.1.0' into 3.1

Conflicts:
	docs/en/changelogs/3.1.1.md
	tests/behat/features/profile.feature
Added 3.1.2 changelog