Correction of merge errors
Simplify integer expressions w extremes: min, max and comparisons

Makefile: Added Type.cpp
Type.h, Type.cpp: Added imax() imin() to return int extremes of integer
types; Added max() min() to return Expr extremes of integer types.
Simplify.cpp: Simplify comparisons and min and max with extremes of the
range of integer data types.  Modify do_indirect_int_cast to use
int_cast_constant, and test to ensure that int_cast_constant is correct.
IROperator.h, IROperator.cpp: Add int_cast_constant and use it when
constructing type cast integer constants to ensure that values are
canonical.