simplify newlocale and allow failure for explicit locale names

simplify newlocale and allow failure for explicit locale names

unify the code paths for allocated and non-allocated locale objects,
always using a tmp object. this is necessary to avoid clobbering the
base locale object too soon if we allow for the possibility that
looking up an explicitly requested locale name may fail, and makes the
code simpler and cleaner anyway.

eliminate the complex and fragile logic for checking whether one of
the non-allocated locale objects can be used for the result, and
instead just memcmp against each of them.