library/bag.m:
The old implementations of bag.subtract, bag.least_upper_bound,
bag.union, bag.intersect iterated over their second bag arguments,
and did a logarithmic amount of work in each iteration. This is good
if the second bag is small, but not if it is big. Keep those
implementations as the implementation of bag.subtract_small,
bag.least_upper_bound_small etc, and replace the implementation
of bag.subtract etc with code that iterates over the assoc_list version
of both bags. This does work that linear in total size of the two sets.
Replace the implementation of bag.subset_compare with one
that actually works.
Replace the implementation of bag.is_subbag with one that
does significantly less work.
Group related predicates together.
Improve the documentation of the exported predicates.
Use a more descriptive and more consistent set of variable names.
tests/hard_coded/test_bag.{m,exp}:
A new test case, to test the new algorithms in bag.m.
tests/hard_coded/Mmakefile:
Enable the new test case.
