Bug 26843: add projects/firefox-locale-bundle

projects/firefox-locale-bundle will clone or pull the mercurial
repositories for each locale into the hg_clones/firefox-locale-bundle
directory, and generate tarballs using the changesets listed in the
firefox json file. The script get_hg_hash is used to parse
this json file and output the hg changeset for the selected locale.

Patch based on work started by GeKo.