Use 'M_CHAR' instead of 'BYTE' to distinguish memory references to characters from those for
bytes. This is needed for Unicode support.
In ASM,SPT, extend code generation for character-related operations to distinguish two cases:
1) CFP_B == CFP_C, for case where character size is byte size
2) CFP_B != CFP_C, for case where character size is word size
This commit passes sanity test for the first case.