git-gui: Refactor the revert (aka checkout-index) implementation.
git-gui: Refactor the revert (aka checkout-index) implementation.

We can revert any file which has a valid stage 0 (is not unmerged)
and which is has a working directory status of M or D.  This vastly
simplifies our pattern matching on file status when building up the
list of files to perform a checkout-index against.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git