* libguile/tags.h (SCM_IM_ELSE, SCM_IM_ARROW): New memoizer codes.

	* libguile/tags.h (SCM_IM_ELSE, SCM_IM_ARROW): New memoizer codes.

	* libguile/print.c (scm_isymnames): Add names for the new memoizer
        codes.

	* libguile/eval.c (s_missing_clauses, s_bad_case_clause,
	s_extra_case_clause, s_bad_case_labels, s_duplicate_case_label,
	literal_p): New static identifiers.

	(scm_m_case): Use ASSERT_SYNTAX to signal syntax errors.  Be more
	specific about the kind of error that was detected.  Check for
	duplicate case labels.  Handle bound 'else.  Avoid unnecessary
	consing when creating the memoized code.

	(scm_m_case, unmemocopy, SCM_CEVAL): Use SCM_IM_ELSE to memoize
	the syntactic keyword 'else.

	* test-suite/tests/syntax.test (exception:bad-expression,
	exception:missing-clauses, exception:bad-case-clause,
	exception:extra-case-clause, exception:bad-case-labels): New.

	Added some tests and adapted tests for 'case' to the new way of
	error reporting.