manifest: make manifest.intersectfiles() internal
manifest.intersectfiles() is just a utility used by manifest.matches(), and
a future commit removes intersectfiles for treemanifest for optimization
purposes.
This commit makes the intersectfiles methods on manifestdict and treemanifest
internal, and converts its test to a more generic testMatches(), which has the
exact same coverage.
$ echo 'raise Exception("bit bucket overflow")' > badext.py
$ abspath=`pwd`/badext.py
$ cat <<EOF >> $HGRCPATH
> [extensions]
> gpg =
> hgext.gpg =
> badext = $abspath
> badext2 =
> EOF
$ hg -q help help
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
hg help [-ec] [TOPIC]
show help for a given topic or a help overview