vim-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.
bfd830d3e2

src/nvim/testdir/test_quotestar.vim

@@ -134,6 +134,6 @@ func Test_quotestar()
   let @* = quotestar_saved
 
   if !empty(skipped)
-    throw skipped
+    throw 'Skipped: ' . skipped
   endif
 endfunc

src/nvim/version.c

@@ -1148,7 +1148,7 @@ static const int included_patches[] = {
   // 494,
   // 493,
   // 492,
-  // 491,
+  491,
   490,
   489,
   // 488,