Split the COMPARE_OP bytecode instruction into four distinct instructions.

*  COMPARE_OP for rich comparisons
*  IS_OP for 'is' and 'is not' tests
*  CONTAINS_OP for 'in' and 'is not' tests
*  JUMP_IF_NOT_EXC_MATCH for checking exceptions in 'try-except' statements.

This improves the clarity of the interpreter and should provide a modest
speedup.
