test-acl: alter sed construct to avoid changes in .hg/hgrc formatting
A future patch is going to add some extra commented-out boilerplate to
the top of .hg/hgrc during clone. In order to make this test not
require regular updates, switch to searching for [hooks] or [acl] and
print file from the first match to that pattern.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.