Log Message:
Set USE_TOOLS instead of BUILD_DEPENDS to get csh, and use ${CSH}
instead of "tcsh". This builds ok for me on NetBSD; if it turns out to
cause trouble for anyone, revert it.

The motivation was that the BUILD_DEPENDS accepted either tcsh or
standalone-tcsh, and distbb was latching onto the latter and then
failing trying to install it. If the package turns out to really need
tcsh in some contexts, there are probably other ways to deal with this
issue.