suggested by and ok stsp@

Parse the "blob -" metadata in diffs produced by 'got diff' and use the original file for patching. Then, use the diff3 with the current version of the file to merge the differences. This solves many failures automagically or at least turns them into a conflict. ok/improvements stsp@

future work with diff3 merge will need the fully patched file even in the nop mode ok stsp@

ok stsp@

ints have the advantage that their size is more likely to be the same across the various architecture supported by OpenBSD, thus introducing less possible differences. INT_MAX is still (at least) a few order of magnitudes higher than the patches we dealt with (even abnormal ones.) suggested by stsp@

previous commit looked at some pretty zeroes returned from calloc instead of the actual numbers received.

under normal circumstances got-read-patch can't send negative line offsets; that's not an excuse not to guard the main process from those as well. This makes sure we bail out early instead of trying to apply the diff.

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.

ok op

add a flag to got_patch to reverse a patch before applying and the -R flag for `got patch'. ok stsp@

as a cheap optimization got-read-patch was sending only the "\ No newline at end of file" lines that follows an addition (a "+" line). To be able to reverse patches in the future got_patch needs to know about all of these lines instead. No functional changes intended. ok stsp@

this allow to apply patches from subdirectories of the work tree root. Prodded by naddy@, ok stsp@.

Move some bits from the libexec helper to the main process so we know if the patch was generated by git or not and finally document the automatic stripping of a/ and b/ prefixes added by git-diff(1). ok stsp@