Users can specify Puppetboard Git SHA to use

Allow a user to specify a Git commit, branch, or tag from Puppetboard's
Git repo. Default value continues to use latest commit.
Add stdlib version requirement to Modulefile

Add requirement on version >= 3.0.0 of stdlib to Modulefile. Version 3.x
of stdlib supports Puppet 2.7.x and Puppet 3. Without this, versions of
librarian-puppet <= 0.9.10 choke.
Merge branch 'stdlib_version'