use src-netbsd instead of rumpkernel-netbsd-src
do no try to commit if we do not have changes

git returns an error for that
handle smallest branch first, quicker way to spot silly errors
note that the git rev stuff needs fixing before merge
Restore ./buildrump.sh checkout behaviour.

Embed the revision id of the buildrump-src branch in buildrump.sh
to control which vintage of sources a given vintage of buildrump.sh uses.
Source for buildrump.sh git rev 01578ef8cbdc986565c6efdf51afaa0063967a60
make checkoutcvs work again