config: give it an includepaths option for looking for config files
It is desirable to "derive" templates from the provided templates. A
simple way to do this is e.g.
in your own mapfile. Then you only have to redefine a few templates
instead of copying over the whole thing. This %include mechanism
already works for the built-in templates because by default it *only*
looks for files that are in the same directory as the including
With this changeset, config grows an option to add more include paths
for config files.