objstr: startswith(): Accept optional "start" arg.
py: More const usage.
py: More mp_identity usage.
py: Fix mp_obj_t -> mp_const_obj_t for mp_obj_int_get_checked()

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>
Merge pull request #615 from swegener/for-upstream

py: Fix mp_obj_t -> mp_const_obj_t for mp_obj_int_get_checked()
intime build
dllexport/loadextlib