patch 8.1.1519: 'backupskip' may contain duplicates

Problem:    'backupskip' may contain duplicates.
Solution:   Add the P_NODUP flag. (Tom Ryder)

src/option.c

@@ -616,7 +616,7 @@ static struct vimoption options[] =
 			    (char_u *)"~",
 #endif
 					    (char_u *)0L} SCTX_INIT},
-    {"backupskip",  "bsk",  P_STRING|P_VI_DEF|P_ONECOMMA,
+    {"backupskip",  "bsk",  P_STRING|P_VI_DEF|P_ONECOMMA|P_NODUP,
 #ifdef FEAT_WILDIGN
 			    (char_u *)&p_bsk, PV_NONE,
 			    {(char_u *)"", (char_u *)0L}
@@ -4807,7 +4807,8 @@ do_set(
 			     * hex numbers. */
 			    vim_str2nr(arg, NULL, &i, STR2NR_ALL,
 						     &value, NULL, 0, TRUE);
-			    if (i == 0 || (arg[i] != NUL && !VIM_ISWHITE(arg[i])))
+			    if (i == 0 || (arg[i] != NUL
+						      && !VIM_ISWHITE(arg[i])))
 			    {
 				errmsg = N_("E521: Number required after =");
 				goto skip;

src/testdir/test_options.vim

@@ -419,6 +419,15 @@ func Test_backupskip()
       call assert_true(found, var . ' (' . varvalue . ') not in option bsk: ' . &bsk)
     endif
   endfor
+
+  " Duplicates should be filtered out (option has P_NODUP)
+  let backupskip = &backupskip
+  set backupskip=
+  set backupskip+=/test/dir
+  set backupskip+=/other/dir
+  set backupskip+=/test/dir
+  call assert_equal('/test/dir,/other/dir', &backupskip)
+  let &backupskip = backupskip
 endfunc
 
 func Test_copy_winopt()

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1519,
 /**/
     1518,
 /**/