Update Vcs fields

Use the canonical URLs. Rename Vcs-Bzr to Vcs-Git and use the more
efficient git protocol instead of http. Point Vcs-Browser to the
gitweb interface.
French translation : typo fix. Closes: #677272
Update changelog to include Vcs-* changes
debian/gbp.conf: add debian-tag key to ensure git-dch works
* buildlib/apti18n.h.in:
  - fix build failure when building without NLS (closes: #671587)
cmdline/apt-key: Create new keyrings with mode 0644 instead of 0600
cmdline/apt-key: Accept nonexistent --keyring file with adv as well