There's no reason to have two different ways of applying patches for whole-file
patches and partial patches; use --reverse for both. Not only does this simplify
the code a bit, but it fixes an actual problem: when reverseOnGenerate and
keepOriginalHeader are both true, the generated patch header is broken (the two
blobs in the line `index 6d1959b..6dc5f84 100644` are swapped). Git fails to do
a proper three-way merge in that case, as it expects the first of the two blobs
to be the common ancestor.
It would be possible to fix this by extending ModifiedPatchForLines to swap the
two blobs in this case; but this would prevent us from concatenating all patches
and apply them in one go, which we are going to do later in the branch.
We are going to add one more flag in the next commit.
Note that we are not using the struct inside patch_manager.go; we keep passing
the individual flags there. The reason for this will become more obvious later
in this branch.
