tests/narrow-library.sh

status: intersect matcher with narrow matcher instead of filtering afterwards

I seem to have done a very naive move of the code from the narrow
extension into core in e411774a2e0f (narrow: move status-filtering to
core and to ctx, 2018-08-02). It seems obvious that a better way is to
intersect the matchers.

Note that this means that when requesting status for the working
directory in a narrow repo, we now pass the narrow matcher (possibly
intersected with a user-provided matcher) into _buildstatus() and then
into dirstate.status() and dirstate.walk(), which will the intersect
it again with the narrow matcher. That's functionally fine, but
wasteful. I hope to later remove the dirstate wrapping that adds the
second layer of matcher intersection.

Differential Revision: https://phab.mercurial-scm.org/D4897

cat >> $HGRCPATH <<EOF
[extensions]
narrow=
[ui]
ssh=python "$TESTDIR/dummyssh"
[experimental]
changegroup3 = True
EOF