Insert a new element to the string_list. The returned pointer can be
handy if you want to write something to the `util` pointer of the
- string_list_item containing the just added string.
+ string_list_item containing the just added string. If the given
+ string already exists the insertion will be skipped and the
+ pointer to the existing item returned.
+
Since this function uses xrealloc() (which die()s if it fails) if the
list needs to grow, it is safe not to check the pointer. I.e. you may