mruby/mruby — pull request #2086 by bovi (2014-04-19 21:47:04+00:00)
Title: Implement :checksum_hash mrbgem option

This allows to use a mgem with a specific checksum hash.
The following modification were necessary to implement this
function:
- add run_checkout build command to use 'git checkout'
- skip shallow copy in case checksum_hash is used
- make 'master' the default branch if branch isn't defined