libpacman: Move list struct definition to private header.
libpacman: Add list item next/previous accessors.
libpacman: Convert a bunch of 'FStringListItem->data' to f_stringlistitem_to_str.
libpacman: More f_stringlistitem_to_str use.
libpacman: Extra list work to remove warning and prepare list implementation change.
libpacman: More global handle access removal.