bug#35420: Support git in ediff-patch-file

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Juri Linkov <juri@linkov.net>,  35420@debbugs.gnu.org
> Date: Thu, 25 Apr 2019 09:53:16 +0200
> 
> You get i/, w/ and/or c/ when you run 'git diff' inside your working
> tree, depending on whether the changed file is in the 'i'ndex,
> 'w'orking tree, or 'c'ache (also known as the staging area). Things
> like 'git format-patch' and 'git show' use a/ and b/ by default.
> 
> And of course, since this is git, you can tell it to use other
> prefixes using '--src-prefix' and '--dst-prefix'.

Thanks.  I guess we'd like to support these use cases as well, right?

Also, what's the situation with hg?  Is it similar?