* backtrace.c (display_expression, display_frame): Call

	* backtrace.c (display_expression, display_frame): Call
	scm_i_unmemoize_expr for unmemoizing a memoized object holding a
	single memoized expression.

	* debug.c (memoized_print): Don't try to unmemoize the memoized
	object, since we can't know whether it holds a single expression
	or a body.

	(scm_mem_to_proc): Removed check for lambda expression, since it
	was moot anyway.  Whoever uses these functions for debugging
	purposes should know what they do: Creating invalid memoized code
	will cause crashes, independent of whether this check is present
	or not.

	(scm_proc_to_mem): Take the closure's code as it is and don't
	append a SCM_IM_LAMBDA isym.  To allow easier debugging, the
	memoized code should not be modified.

	* debug.[ch] (scm_unmemoize, scm_i_unmemoize_expr): Removed
	scm_unmemoize from public use, but made scm_i_unmemoize_expr
	available as a guile internal function instead.  However,
	scm_i_unmemoize_expr will only work on memoized objects that hold
	a single memoized expression.  It won't work with bodies.

	* debug.c (scm_procedure_source), macros.c (macro_print), print.c
	(scm_iprin1): Call scm_i_unmemocopy_body for unmemoizing a body,
	i. e. a list of expressions.

	* eval.c (unmemoize_exprs): Drop internal body markers from the
	output during unmemoization.

	* eval.[ch] (scm_unmemocopy, scm_i_unmemocopy_expr,
	scm_i_unmemocopy_body): Removed scm_unmemocopy from public use,
	but made scm_i_unmemocopy_expr and scm_i_unmemocopy_body available
	as guile internal functions instead.  scm_i_unmemoize_expr will
	only work on a single memoized expression, while
	scm_i_unmemocopy_body will only work on bodies.