git-gui: Correct unmerged file detection at commit time.

git-gui: Correct unmerged file detection at commit time.

Its impossible to commit an index which has unmerged stages.

Unfortunately a bug in git-gui allowed the user to try to do exactly that,
as we broke out of our file scanning loop as soon as we found a valid AMD
index state.  That's wrong, as the files are coming back from our array
in pseudo-random order; an unmerged file may get returned only after all
merged files.

I also noticed the grammer around here in our dialog boxes still used
the term 'include', so this has been updated to reflect current usage.

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