Allow a static build of redis
Allow libgit2 location override for redis backend
Updated odb backend to current libgit2
Added redis refdb backend
Fix reference iteration mask
Added authentication support for redis
Reuse a single redis connection
Fix prefix and repo_path memory management
fix reference iteration, take 2
Minor cmake fix
Don't use OBJECT in CMakeLists.txt
Reference iteration, take 3

Hopefully correct this time:
- iterating with globs assumes the glob is a full name, e.g. 'refs/heads/test-*' or 'H*'
- iterating without a glob uses a default glob of 'refs/*'
Remove awful useless cmake stuff
Don't use pkg-config to find libgit2

This may be wrong, but turning off pkg-config in FindLibgit2.cmake
makes cmake respect library paths given from the command line (with -D)
Update refdb to new API
Merge pull request #5 from redbadger/redis-backend

Update the redis backend