tests/test-revert-flags.t

archival: don't set gzip filename header when there's no filename

This mainly affects hgweb, which can generate tar.gz archives without
filenames. Without this change, the header would be set to ".gz",
which can confuse Safari into extracting the file and renaming it to
"gz" when "Open 'safe' files after downloading" is enabled.

file(1) before:

hg-crew-5e51254ad4d4.tar.gz: gzip compressed data, was ".gz", last modified: Thu Dec  2 11:46:20 2010, max compression

after:

hg-crew-5e51254ad4d4.tar.gz: gzip compressed data, last modified: Thu Dec  2 11:46:20 2010, max compression

  $ "$TESTDIR/hghave" execbit || exit 80

  $ hg init repo
  $ cd repo
  $ echo foo > foo
  $ chmod 644 foo
  $ hg ci -qAm '644'

  $ chmod 755 foo
  $ hg ci -qAm '755'

reverting to rev 0

  $ hg revert -a -r 0
  reverting foo
  $ hg st
  M foo
  $ hg diff --git
  diff --git a/foo b/foo
  old mode 100755
  new mode 100644