* libguile/eval.c (s_missing_expression, s_bad_variable): New static

	* libguile/eval.c (s_missing_expression, s_bad_variable): New static
	identifiers.

	(scm_m_define): Use ASSERT_SYNTAX to signal syntax errors.  Prefer
	R5RS terminology for the naming of variables.  Be more specific
	about the kind of error that was detected.  Make sure file name,
	line number etc. are added to all freshly created expressions.
	Avoid unnecessary consing when creating the memoized code.

	* test-suite/tests/syntax.test (exception:missing-expr,
	exception:extra-expr): New.

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