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/cmdexpand.c b/src/cmdexpand.c
index b0ea057..9508d66 100644
--- a/src/cmdexpand.c
+++ b/src/cmdexpand.c
@@ -1728,7 +1728,8 @@
 	    {
 		if ( STRNCMP(arg, "messages", p - arg) == 0
 		  || STRNCMP(arg, "ctype", p - arg) == 0
-		  || STRNCMP(arg, "time", p - arg) == 0)
+		  || STRNCMP(arg, "time", p - arg) == 0
+		  || STRNCMP(arg, "collate", p - arg) == 0)
 		{
 		    xp->xp_context = EXPAND_LOCALES;
 		    xp->xp_pattern = skipwhite(p);