libflib: Do not call FVisitor::fn when NULL in f_visit.
libflib: Create FListItem of FList item based function.
libflib: Add f_list_begin/end paradigms, move f_list_count.
libflib: Make flib list more iterator style.
libflib: Rename f_list_next/previous to f_listitem.
libflib: Add f_list_add, f_list_append_unique and reorganise the code a little.
libflib: Add _pacman_trans_remove_target.
libflib: Some libflib flist changes, prepare deprecation of some functions.