patch 8.1.0017: shell command completion has duplicates

Problem:    Shell command completion has duplicates. (Yegappan Lakshmanan)
Solution:   Use a hash table to avoid duplicates. (Ozaki Kiichi, closes #539,
            closes #2733)

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    17,
 /**/
     16,
 /**/