hgweb: add compatibility code for old templates
Up to changeset
3340aa5a64f7, HTTP headers were expected to be embedded
in the "headers" template. Since that changeset, the content-type is
supposed to be defined as the "mimetype" template in the map file.
This changeset makes sure the old templates still work.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.