My patch of a couple of days ago to prohibit a parenthesized argument to
a go or defer statement was faulty.  I tested whether the expression
starts with a parenthesis, but of course there are valid function calls
that start with a parenthesis but for which the entire expression is not
parenthesized.  This patch fixes that oversight.  Bootstrapped and ran
Go testsuite on x86_64-unknown-linux-gnu.  Committed to mainline.

Ian