Changes to smooth out make_release

Changes to smooth out make_release

1) Make the fake 'HeadURL' into a URL which works with our web repo.
Note that this has 'tags/' hardcoded in, so it only works with true
release branches (e.g. rel_x_y_z) not "working" branches
(e.g. rel_x_y).

2) Change range selector when building log to exclude commits from
rel_2_4.

3) Switch the XULRunner download order so that we can remove them
automatically during make_release and manually afterwards.

4) Add a pause between tagging and building for manual tweaks.

Signed-off-by: Dan Wells <dbw2@calvin.edu>