call free() on the util members of any items that have to be
deleted. Preserve the order of the items that are retained.
-`string_list_longest_prefix`::
-
- Return the longest string within a string_list that is a
- prefix (in the sense of prefixcmp()) of the specified string,
- or NULL if no such prefix exists. This function does not
- require the string_list to be sorted (it does a linear
- search).
-
`print_string_list`::
Dump a string_list to stdout, useful mainly for debugging purposes. It