complete: disable folding when completing

Fixes vim/vim#643

test/functional/viml/completion_spec.lua

@@ -141,4 +141,10 @@ describe('completion', function()
         June]])
     end)
   end)
+
+  it('disables folding during completion', function ()
+	  execute("set foldmethod=indent")
+	  feed('i<Tab>foo<CR><Tab>bar<Esc>ggA<C-x><C-l>')
+	  eq(-1, eval('foldclosed(1)'))
+  end)
 end)