WyC: Removed notion of Implicit Coercion #418.

This is currently not complete, in the sense that lots of test cases are
currently failing.  These need to be further inspected and updated.
WyC: Removed Implicit Coercions from Tests #418

Working through valid test cases and eliminating any use of implicit
coercions.  As a result, there are some test cases which no longer make
sense.  There are also some test cases for which we need to figure out
what the right option is.
WyC: Removed Implicit Coercions from Tests #418

Working through valid test cases and eliminating any use of implicit
coercions.  As a result, there are some test cases which no longer make
sense.  There are also some test cases for which we need to figure out
what the right option is.
WyC: Updating char type to support arithmetic.

As part of #418, have updated char datatype to support binary
arithmetic.  Need to complete this for other operators.
WyC: Updated char type to support all operators.

The char type now supports all arithmetic and comparator operators as
part of #418.  In addition, the error messages have been improved in the
case of incomparable operands, etc.
WyC: Bug fixes for updated char type #418.

Some minor bug fixes related to updating char type to support arithmetic
and comparators.
WyC: Very minor tweak to prevent char negation #418.

It never makes sense to have a negative character value.  Therefore, I
have prevented the possibility by disallowing char type for use with the
negation operator.
WyC: Updated more test cases for #418.

Have made additional changes to test cases which are invalid under
changes for #418.  Typical modifications include inserting casts to make
previously implicit coercions explicit.  There are still a number of
outstanding problems, however.
WyC: Updated sublist operator for #418

The sublist operator now correctly handles the distinction between lists
and strings, which was exposed by #418.
WyC: AllValidTests are now passing.  #418

Unfortunately, there are still changes to push through.  Some invalid
tests are not passing, and WyJC doesn't compile.
WyC: AllInvalidTests now pass #418.

Updated test cases which were invalidated by the loss of implicit
coercions.  Most of the updates involved putting explicit casts in place
of previously implicit ones.
WyJC: Minimal fix to support char arithmetic #418.

This fix is something of a kludge, but it should work OK.  Basically
I've special-cased the char type for the arithmetic operators.
WyJC: Temporary fix for coercing strings #418

This fix is for the case where a string is coerced into a set.  In
reality, I think this coercion is invalid in some sense.  However, for
now, we'll leave it.
WyC: Updated final test case for #418.

At this point, #418 is now complete.
Merge branch 'features/418-coercions'