Do not allow git_branch_create() to force update branch
Add unit test to show git_branch_create() fails if attempt to force create current branch
Merge pull request #2144 from linquize/branch-f-current

Do not allow git_branch_create() to force update branch
caps: Rename to features to avoid confusion
caps: Rename the enum name too!
features: Rename `_HAS_` to `_FEATURE_`
Merge pull request #2150 from libgit2/vmg/features

caps: Rename to features to avoid confusion