Minor changes for lein-release.

* Adds 'commit' multimethod and :git impelementation.'
* Use binding on leiningen.release/*level* to pass release task arg to default
  :release-tasks.
Update :git commit method.

Necessary for default release-tasks.

Signed-off-by: Wayne <wayne@puppetlabs.com>
Fix passing of stale project map bug.

Since release-tasks could include any number of lein-change calls, seems like a
good idea to re-read project.clj between tasks.

Signed-off-by: Wayne <wayne@puppetlabs.com>
Merge remote-tracking branch 'waynr/lein-release'

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# the commit.
Make bump-version work with strings and default to bound *level*.