print SRCDIR/DESTDIR/OBJDIR/BRTOOLDIR too (for completeness)
Set the directory defaults in parseargs

This, in addition to being consistent, prevents someone from
accidentally using the default values before actual values are set.
update URL (anttikantee -> rumpkernel)
cherry-pick a bugfix to make, makes MAKEOBJDIR work on FreeBSD
Source for buildrump.sh git rev 7f26985450eba0234f2774e0705a5acae8f53d99