Major code reoganisation, splitting up the single big file. The two goals

Major code reoganisation, splitting up the single big file. The two goals
kept in mind during this are a) to reduce load time for common cases like
cgi and post-commit and b) make the code easier to navigate.

This also modularises RCS support to the extent that it should be possible
to drop in a module for some RCS other than svn, add a switch for it, and
it pretty much just work.

High chance I missed an edge case that breaks something, this is only
barely tested at this point.