When working with a lot of people who backport patches all day long, every
once in a while I get a patch that modifies the same file more than once
inside the same patch.  git-apply either fails if the second change relies
on the first change or silently drops the first change if the second change
is independent.

The silent part is the scary scenario for us.  Also this behaviour is
different from the patch-utils.

I have modified git-apply to create a table of the filenames of files it
modifies such that if a later patch chunk modifies a file in the table it
will buffer the previously changed file instead of reading the original file
from disk.

Logic has been put in to handle creations/deletions/renames/copies.  All the
relevant tests of git-apply succeed.

A new test has been added to cover the cases I addressed.

The fix is relatively straight-forward.
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>