Correctly handle detached head for 'latest' on latest Git versions

[mikegerwitz]

Newer versions of Git (I'm not sure as of what version) will output the following for git branch -a while in a detached HEAD state:

$ git branch -a
* (detached from 4689c51)                                             
  master                                                              
  remotes/origin/HEAD -> origin/master

The first line is different than what is expected from previous Git version: "(no branch)". This patch uses rev-parse, which should work with most existing Git versions and will hopefully be immune to this problem in the future.

This patch also gets rid of "origin/HEAD", which is not a valid (and does throw an error in newer Git versions); origin/master points to the tip of master on origin, which seems to be what was desired.

[hopperd]

Nice Mike, this fixes an that annoying issue that we've been having!

[apenney]

I'd love to get this merged but unfortunately it's breaking the travis tests. Any chance you can have a quick stab at fixing the unit tests?

[mikegerwitz]

Sorry about that; I'll take care of it now. Haven't written a line of ruby before, so just need to get a working environment first so that I can run those tests.

[mikegerwitz]

The tests have been corrected. Please note that I amended the tip of my master branch.

[apenney]

Thanks for taking this on so quickly, and for the patch!

[mikegerwitz]

And thank you for merging that so quickly.