* debug.c (scm_m_start_stack): Bugfix: Use SCM_ECONSP instead of

* debug.c (scm_m_start_stack): Bugfix: Use SCM_ECONSP instead of
SCM_CONSP since this is a macro!; Set vframe.prev to
scm_last_debug_frame instead of 0.  In this way we can look
"above" the virtual start stack frame if we wish.
(scm_debug_hang): New function: Useful for debugging Guile in
certain tricky situations.  Will probably be removed later...