Log Message: 
Added ability for Unions and Sets to simplify themselves
(automatically or on demand), and added flags to the Context and
answer checkers to control these features. The new Context flags
are
reduceUnions tells whether unions are automatically
reduced when they are created.
reduceUnionsForComparison tells whether unions are reduced
before comparing them for equality
or inequality (etc) if they aren't
reduced already.
reduceSets tells whether redundent elements are
removed from sets as they are created.
reduceSetsForComparison tells whether sets are reduced before
comparing them.
All of these default to true.
The Interval, Set, Union, and List answer checkers not have two new
flags for controlling these values:
studentsMustReduceUnions tells whether unions and sets will be
counted as incorrect when they are not
reduced to nonoverlapping intervals
and at most one set with no repeated
entries.
showUnionReduceWarnings tells whether an error message will
be produced for nonreduced unions and
sets, or if they will be marked wrong
silently. (Not available in Lists.)
Both of these are true by default, since most professors probably want
their students to write intervals in reduced form. (Is this true?)
This corresponds the the current behavior of the interval checkers,
which require the student's answer to be the same set of intervals as
in the professor's, but with the addition of an error message when the
student answer is not reduced.
