* libguile/eval.c (s_duplicate_binding): New static identifier.

	* libguile/eval.c (s_duplicate_binding): New static identifier.

	(scm_m_case): Call scm_c_memq instead of implementing it inline.

	(scm_m_define): Added comment about how we check for duplicate
	formals.

	(scm_m_do): Added check for duplicate bindings.

	(scm_m_if): Use ASSERT_SYNTAX to signal syntax errors.  Avoid
	unnecessary consing when creating the memoized code.

	(scm_c_improper_memq, c_improper_memq, scm_m_lambda): Renamed
	scm_c_improper_memq to c_improper_memq, since it is not exported.

	(transform_bindings): Call scm_c_memq rather than
	scm_c_improper_memq.

	(SCM_CEVAL): Simplified handling of SCM_IM_IF forms.

	* test-suite/tests/syntax.test (exception:missing/extra-expr-syntax):
        New, introduced temporarily until all memoizers use the new way of
	error reporting.

	Adapted tests for 'if' to the new way of error reporting.