patch 9.0.0003: functions are global while they could be local

Problem:    Functions are global while they could be local.
Solution:   Add "static".  Add a few tests. (Yegappan Lakshmanan,
            closes #10612)

src/scriptfile.c

@@ -2346,7 +2346,7 @@ source_finished(
  * Find the path of a script below the "autoload" directory.
  * Returns NULL if there is no "/autoload/" in the script name.
  */
-    char_u *
+    static char_u *
 script_name_after_autoload(scriptitem_T *si)
 {
     char_u	*p = si->sn_name;