Represent 'unit' as C 'int'; change pattern match compilation to avoid 'goto'; change Postgres prepared statement compilation to make life easier for the GCC escape analysis; all this in support of better tail call optimization

fun main () : transaction page =
    ua <- requestHeader "User-Agent";
    case ua of
        None => return <xml>Not found</xml>
      | Some s => return <xml>User-Agent: {[s]}</xml>