My commit to reset committer info during rebase was too strict in some use cases. Even when simply forwarding a branch the rebase operation could now fail if GOT_AUTHOR is not set. To fix this, fall back on existing commiter information if no author is configured. And try to obtain author info from Git config in case GOT_AUTHOR is not set. Problems reported by Mikhail.

ok op@

OK stsp

Found by llvm's scan-build (dead store). OK stsp

Make the choice of diff algorithm configurable by diff API users. The got and gotweb programs keep using Patience diffs which are prettier than Myers. But tog should be as fast as possible since it is being used interactively. If performance of Patience diff gets improved later we can consider switching tog back over to it. ok tracey jamsek

ok tracey

ok tracey

ok stsp@

otherwise we end up with a staged empty edit for that file. ok stsp@

ok tracey

let got_patch own fileindex_path and call got_worktree_patch_complete only if got_wokrtree_patch_prepare hasn't failed. suggested by stsp@

Instead of flushing the fileindex after every patch in the patchfile just reuse the same fileindex and sync it only at the end of the patch operation. This speeds up 'got patch' on large repositories by quite a lot.