(buffer_permanent_local_flags): Make a char array.

(buffer_permanent_local_flags): Make a char array.
(max_buffer_local_idx): New variable.
(reset_buffer_local_variables, Fbuffer_local_variables): Rewritten
for new handling of per-buffer variables.
(buffer_slot_type_mismatch): Use new macros for per-buffer vars.
(init_buffer_once): Initialize per-buffer vars differently.
Set max_buffer_local_idx.