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/filepath.pro b/src/proto/filepath.pro
index a3df123..405c8b5 100644
--- a/src/proto/filepath.pro
+++ b/src/proto/filepath.pro
@@ -20,6 +20,7 @@
 void f_globpath(typval_T *argvars, typval_T *rettv);
 void f_isdirectory(typval_T *argvars, typval_T *rettv);
 void f_mkdir(typval_T *argvars, typval_T *rettv);
+void f_pathshorten(typval_T *argvars, typval_T *rettv);
 void f_readdir(typval_T *argvars, typval_T *rettv);
 void f_readfile(typval_T *argvars, typval_T *rettv);
 void f_resolve(typval_T *argvars, typval_T *rettv);