Revision 1902906

core: Follow up to r1902728: pools may have no allocator with APR_POOL_DEBUG.

With APR <= 1.7 and APR_POOL_DEBUG, thread's pools don't necessarily have an
allocator, so avoid apr_allocator_max_free_set(NULL) in ap_thread_create() and
ap_thread_main_create().

Also, always create an allocator in ap_thread_current_create().