Remove the deprecated :rubyforge source in Gemfiles

Replce with secure 'https://rubygems.org'
Make sure the correct version of Psych is present for ruby 1.9.2
Strip the :default param from missing translations when current locale isn't the default locale
Merge branch 'refs/heads/pr99'
Update README.md

Locale no longer accepts importing .zip files, but pushing a whole directory is possible.
cache missing translations
Refactor MissingTranslation#cached_keys so that we're not using a class variable

Also add a spec for when we're NOT cacheing missing translations
Minor tweak to the README
Reapplied PR #99 after merge with master (don't send translationsn for non-default locales)