index: handle index[-1] as nullid more explicitly
I find it more intuitive to check if "pos == -1" than to first add the
index length (which includes one extra item for the nullid) and
compare that to "length - 1". However, because test-parseindex2.py
compares the whole index (up to len(index)-1), we need to also
preserve that other check for a little while more. I'll remove it
soon.
Differential Revision: https://phab.mercurial-scm.org/D4018
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown