patch 8.0.0491: quotestar test fails when features are missing

Problem:    The quotestar test fails when a required feature is missing.
Solution:   Prepend "Skipped" to the thrown exception.
diff --git a/src/testdir/test_quotestar.vim b/src/testdir/test_quotestar.vim
index 300a964..111a226 100644
--- a/src/testdir/test_quotestar.vim
+++ b/src/testdir/test_quotestar.vim
@@ -134,6 +134,6 @@
   let @* = quotestar_saved
 
   if !empty(skipped)
-    throw skipped
+    throw 'Skipped: ' . skipped
   endif
 endfunc
diff --git a/src/version.c b/src/version.c
index e009e8e..50b7c4a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    491,
+/**/
     490,
 /**/
     489,