Prevent Sha regeneration in the OdbBackend
Allow handling of odd-sized short Shas in OdbBackend
Refactor OdbBackEnd
Teach repo.ObjectDatabase to enumerate GitObjects
Fix OdbBackEnd ForEach prototype
Introduce RewriteHistoryOptions

RewriteHistory's multiple optional parameters make evolving the API
difficult. In particular, there was no way to change the parent
rewriter to operate on the full commit without a breaking change
(due to ambiguous overloads with sparse parameter use).
Map rewritten parents to rewritten commits
odb_foreach() issue
add [In] attribute on callback function

Fixes the issue on Windows, not on Mono?