The last part is the stuff to hook it in from assign_wrapper, and some
additional support in assign that Rob is adding for me. This comment is
from the top of new file db/libadminctrl.pm.in and describes everything in
detail.

# Admission control policies. These are the ones I could think of, although
# not all of these are implemented.
#
#  * Number of experiments per type/class (only one expt using robots).
#
#  * Number of experiments per project
#  * Number of experiments per subgroup
#  * Number of experiments per user
#
#  * Number of nodes per project      (nodes really means pc testnodes)
#  * Number of nodes per subgroup
#  * Number of nodes per user
#
#  * Number of nodes of a class per project
#  * Number of nodes of a class per group
#  * Number of nodes of a class per user
#
#  * Number of nodes of a type per project
#  * Number of nodes of a type per group
#  * Number of nodes of a type per user
#
#  * Number of nodes...