revlog: list older-but-still-around file in `files`
These older files will eventually be removed, but we have to take them in account until they are. So we update `files` to keep fncache happy.
Differential Revision: https://phab.mercurial-scm.org/D10868
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..