* macroexp.c (init_buffer, gather_arguments, expand): Use NULL, not 0.

* macroexp.c (init_buffer, gather_arguments, expand): Use NULL, not 0.
* macrotab.c (macro_lookup_inclusion, find_definition,
new_macro_table): Same.

* macroexp.c (currently_rescanning, expand): Use `strcmp () == 0',
not `! strcmp ()'.  This is a dubious improvement.
* macrotab.c (macro_lookup_inclusion, find_definition): Same.

* macrotab.c (macro_lookup_inclusion): Initialize `best_depth',
although it's not necessary, to avoid a warning.