tests/test-archive.out

run-tests.py: fix diff output when test-foo.out doesn't exist.

Previously, if test-foo.out doesn't exist and test-foo outputs
something, the first line of the diff will look like this:

-+changeset:   0:0acdaf898367

(note the leading "-")

(the addremove command is deprecated; use add and remove --after instead)
adding foo
(the addremove command is deprecated; use add and remove --after instead)
adding bar
(the addremove command is deprecated; use add and remove --after instead)
adding baz/bletch
test-archive-TIP/.hg_archival.txt
test-archive-TIP/bar
test-archive-TIP/baz/bletch
test-archive-TIP/foo
test-archive-TIP/.hg_archival.txt
test-archive-TIP/bar
test-archive-TIP/baz/bletch
test-archive-TIP/foo
Archive:  archive.zip
    testing: test-archive-TIP/.hg_archival.txt   OK
    testing: test-archive-TIP/bar   OK
    testing: test-archive-TIP/baz/bletch   OK
    testing: test-archive-TIP/foo   OK
No errors detected in compressed data of archive.zip.
test/.hg_archival.txt
test/bar
test/baz/bletch
test/foo
test/.hg_archival.txt
test/bar
test/foo
test-TIP/.hg_archival.txt
test-TIP/bar
test-TIP/baz/bletch
test-TIP/foo
abort: archive prefix contains illegal components
Archive:  test.zip
    testing: test/.hg_archival.txt    OK
    testing: test/bar                 OK
    testing: test/baz/bletch          OK
    testing: test/foo                 OK
No errors detected in compressed data of test.zip.
test-TIP/.hg_archival.txt
test-TIP/bar
test-TIP/baz/bletch
test-TIP/foo