bookmark: do not crash when active bookmark is forward and --date is used
The logic that decides where to update according to the active bookmark
location (when not on ".") was setting the rev to update to before we process
--date. This lead to --date processing aborting because of duplicated
specification.
We reorder the two pieces of code and add a test for this.
To run the tests, do:
cd tests/
python run-tests.py
See http://mercurial.selenic.com/wiki/WritingTests for
more information on writing tests.