tests/test-revlog-packentry

bookmarks: Avoid unconditional forwarding of bookmarks for the null revision

This patch fixes the following minor problem:

% hg bookmark -r null test
% hg bookmarks
   test                      -1:000000000000
[...]
% hg commit
% hg bookmarks
 * test                      17:861ce7a241f9

That is: Bookmarks referring to the null revision are always forwarded
to the current revision.

#!/bin/sh

hg init repo
cd repo

touch foo
hg ci -Am 'add foo'

hg up -C null
# this should be stored as a delta against rev 0
echo foo bar baz > foo
hg ci -Am 'add foo again'

hg debugindex .hg/store/data/foo.i