patch 8.1.1989: the evalfunc.c file is still too big

Problem:    The evalfunc.c file is still too big.
Solution:   Move f_pathshorten() to filepath.c.  Move f_cscope_connection() to
            if_cscope.c.  Move diff_ functions to diff.c.  Move timer_
            functions to ex_cmds2.c.  move callback functions to evalvars.c.
diff --git a/src/proto/diff.pro b/src/proto/diff.pro
index 2ab6c54..b18c59b 100644
--- a/src/proto/diff.pro
+++ b/src/proto/diff.pro
@@ -27,4 +27,6 @@
 int diff_move_to(int dir, long count);
 linenr_T diff_get_corresponding_line(buf_T *buf1, linenr_T lnum1);
 linenr_T diff_lnum_win(linenr_T lnum, win_T *wp);
+void f_diff_filler(typval_T *argvars, typval_T *rettv);
+void f_diff_hlID(typval_T *argvars, typval_T *rettv);
 /* vim: set ft=c : */