The LastCommitCache code is a little complex and there is unnecessary
duplication between the gogit and nogogit variants.
This PR adds the LastCommitCache as a field to the git.Repository and
pre-creates it in the ReferencesGit helpers etc. There has been some
simplification and unification of the variant code.
Signed-off-by: Andrew Thornton <art27@cantab.net>
This PR continues the work in #17125 by progressively ensuring that git
commands run within the request context.
This now means that the if there is a git repo already open in the context it will be used instead of reopening it.
Signed-off-by: Andrew Thornton <art27@cantab.net>
