patch 8.2.0988: getting directory contents is always case sorted

Problem:    Getting directory contents is always case sorted.
Solution:   Add sort options and v:collate. (Christian Brabandt, closes #6229)
diff --git a/src/evalfunc.c b/src/evalfunc.c
index fe98636..230962e 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -769,8 +769,8 @@
 			},
     {"rand",		0, 1, FEARG_1,	  ret_number,	f_rand},
     {"range",		1, 3, FEARG_1,	  ret_list_number, f_range},
-    {"readdir",		1, 2, FEARG_1,	  ret_list_string, f_readdir},
-    {"readdirex",	1, 2, FEARG_1,	  ret_list_dict_any, f_readdirex},
+    {"readdir",		1, 3, FEARG_1,	  ret_list_string, f_readdir},
+    {"readdirex",	1, 3, FEARG_1,	  ret_list_dict_any, f_readdirex},
     {"readfile",	1, 3, FEARG_1,	  ret_any,	f_readfile},
     {"reduce",		2, 3, FEARG_1,	  ret_any,	f_reduce},
     {"reg_executing",	0, 0, 0,	  ret_string,	f_reg_executing},