layouts: add custom layout for those of us that need weird mappings This adds a config-driven custom layout, targeted at the case where you need to fetch a small subset of a large number of subversion branches, or where your subversion layout doesn't match the standard trunk/branches/tags layout very well.

include Makefile hgsubversion/help/*.rst tests/fixtures/invalid_utf8.tar.gz
recursive-include tests *.py *.sh *.svndump *.txt