convert_tuple_to_char_pointer_array now also accepts lists and not only
tuples when converting to a C array. Other fixes:

 - some checking that it's actually a list/tuple before trying to
   convert
 - off-by-a-few-bytes allocation error
   (sizeof(char *)*n+1 vs. sizeof(char *)*(n+1)/calloc(...))
Signed-off-by: Christian Seiler <christian@iwakd.de>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>