This moves CVS, P4, and SVN support to three subports,
so that they're not built by default, but can be installed
as binary packages that depend on devel/git.
Things were done in a way, so that the port can be
maintained from within devel/git.
Did some testing, could use some more love.
This looks like it's more for debugging than for an end user. Maybe put this under boot verbose? The reason is that it's not an error until it's an error, meaning that if we're going to wait for the device when it's not there yet, then printing errors is confusing. Putting it under boot verbose is a nice way for people to get insight into why a boot may be stalled...