add check_key to get_multi_raw, and add a testcase
add another testcase to confirm fixing
make up missing change.
Merge pull request #24 from lilinghui/python-libmemcached:fix_get_multi

fix get_multi_raw's bug
让 get_multi 的参数 keys 可以是任意的 iterable
Merge pull request #25 from satoru/python-libmemcached:accept_iterable

让 get_multi 的参数 keys 可以是任意的 iterable
make delete_multi has same behaviour as delete.
Merge pull request #26 from lilinghui/python-libmemcached:fix_delete_multi

make delete_multi has same behaviour as delete.