patch 8.1.0897: can modify a:000 when using a reference

Problem:    Can modify a:000 when using a reference.
Solution:   Make check for locked variable stricter. (Ozaki Kiichi,
            closes #3930)
diff --git a/src/proto/eval.pro b/src/proto/eval.pro
index 1e673e3..ba75f07 100644
--- a/src/proto/eval.pro
+++ b/src/proto/eval.pro
@@ -103,8 +103,8 @@
 int var_check_ro(int flags, char_u *name, int use_gettext);
 int var_check_fixed(int flags, char_u *name, int use_gettext);
 int var_check_func_name(char_u *name, int new_var);
+int var_check_lock(int lock, char_u *name, int use_gettext);
 int valid_varname(char_u *varname);
-int tv_check_lock(int lock, char_u *name, int use_gettext);
 void copy_tv(typval_T *from, typval_T *to);
 int item_copy(typval_T *from, typval_T *to, int deep, int copyID);
 void get_user_input(typval_T *argvars, typval_T *rettv, int inputdialog, int secret);