138 version switch

Attempt to resolve pull request #138 - "--version option invokes help command".

Two simple changes:
* Added a description of the version switch into the help text.
* Changed app behavior to simply display "appname version versionno" (e.g., git version 1.8.1) when the --version global switch is used. Previous behavior was to display the help text.

Changed a few cucumber features to reflect the changes. Added a new scenario to test the new feature. All pass, as do tests. All changes are in a "138-version-switch" branch, which should merge into the gli-2 branch as of this date.