dirstate: avoid use of zip on big lists
In a clean working directory containing 170,000 tracked files, this
improves performance of "hg --time diff" from 1.69 seconds to 1.43.
This idea is due to Siddharth Agarwal.
$ "$TESTDIR/hghave" pyflakes || exit 80
$ cd "`dirname "$TESTDIR"`"
$ pyflakes mercurial hgext 2>&1 | "$TESTDIR/filterpyflakes.py"
hgext/inotify/linux/__init__.py:*: 'from _inotify import *' used; unable to detect undefined names (glob)