Enhance git support

Added a couple of git related modes to the default distribution:

* git-commit-mode
* gitconfig-mode
* gitignore-mode
Add a sensible .projectile file to the project
Shameless self-plug :-)
guru shmuru
Merge branch 'upstream' into dfc-prelude

* upstream:
  Shameless self-plug :-)
  Add a sensible .projectile file to the project
  Enhance git support