Make it possible to disable filtering for a pattern.
Rationale: Apparently there were no way to disable for example win32text extension locally.
RFC: Can it already be done another way?
#!/bin/sh
"$TESTDIR/hghave" symlink || exit 80
echo "[extensions]" >> $HGRCPATH
echo "mq=" >> $HGRCPATH
hg init
hg qinit
hg qnew base.patch
echo a > a
echo b > b
hg add a b
hg qrefresh
$TESTDIR/readlink.py a
hg qnew symlink.patch
rm a
ln -s b a
hg qrefresh --git
$TESTDIR/readlink.py a
hg qpop
hg qpush
$TESTDIR/readlink.py a