r20600 broke mailer.py's diff url promises

mailer.py's sample configuration file -- and, until r20600, behavior --
gives the following expected behavior for the diff_*_url options:

   # Diff URL construction. For the configured diff URL types, the diff
   # section (which follows the message header) will include the URL
   # relevant to the change type, even if actual diff generation for that
   # change type is disabled (per the generate_diffs option).
   #
   # Available substitution variables are: path, base_path, rev, base_rev

But as of r20600, those substitution variables (path, base_path, rev,
base_rev) no longer work.

I haven't really jumped into a debugging session, but my guess is that the
substitution is now happening earlier than it was before (in the calls to
cfg.get()), specifically, too early for the above variables to have been
defined.

I'm tracking this regression in issue #2587.

-- 
C. Michael Pilato <cmpilato@collab.net>
CollabNet   <>   www.collab.net   <>   Distributed Development On Demand