mcs/parser: make it so that an incomplete statement without a semicolon

mcs/parser: make it so that an incomplete statement without a semicolon
continue parsing as if there was a brace as the next token in the stream.

This allows the following sample to report only the missing semicolon
as error 1525:

using System;
class Program
{
   public static void Main ()
   {
       TestMethod (delegate (object sender, EventArgs args) {

       })
   }
}

Instead of reporting both 1525 and later on a second 1525 for the
end-of-file token