Make int(b'123') work properly.
Merge branch 'int-bytes' of https://github.com/dhylands/micropython into dhylands-int-bytes
py: Improve efficiency of MP_OBJ_IS_STR_OR_BYTES.

Saves ROM (16 on stmhal, 240 on 64-bit unix) and should be quicker since
there is 1 less branch.
Merge branch 'dhylands-int-bytes'