patch 8.2.0049: command line completion not fully tested

Problem:    Command line completion not fully tested.
Solution:   Add more test cases.  Make help sorting stable. (Dominique Pelle,
            closes #5402)
diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 4910491..c8a93bc 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -5341,10 +5341,18 @@
 {
     char    *p1;
     char    *p2;
+    int	    cmp;
 
     p1 = *(char **)s1 + strlen(*(char **)s1) + 1;
     p2 = *(char **)s2 + strlen(*(char **)s2) + 1;
-    return strcmp(p1, p2);
+
+    // Compare by help heuristic number first.
+    cmp = strcmp(p1, p2);
+    if (cmp != 0)
+	return cmp;
+
+    // Compare by strings as tie-breaker when same heuristic number.
+    return strcmp(*(char **)s1, *(char **)s2);
 }
 
 /*