* libguile/eval.c (s_extra_expression, s_misplaced_else_clause,

	* libguile/eval.c (s_extra_expression, s_misplaced_else_clause,
	s_bad_cond_clause, s_missing_recipient): New static identifiers.

	(s_extra_case_clause): Removed.

	(scm_m_case, scm_m_cond): If a clause appears after an else
	clause, report a misplaced else clause.

	(scm_m_cond): Use ASSERT_SYNTAX to signal syntax errors.  Be more
	specific about the kind of error that was detected.  Handle bound
	'else and '=>.  Avoid unnecessary consing when creating the
	memoized code.

	(scm_m_cond, unmemocopy, SCM_CEVAL): Use SCM_IM_ELSE to memoize
	the syntactic keyword 'else and SCM_IM_ARROW to memoize the
	syntactic keyword '=>.

	* test-suite/tests/syntax.test (exception:misplaced-else-clause,
	exception:bad-cond-clause): New.

	(exception:bad/missing-clauses, exception:extra-case-clause):
	Removed.

	Adapted tests for 'case' and 'cond' to the new way of error
	reporting.

	The tests that check if cond is hygienic pass now.