Garbage collection
 - be sure to mark all contained scm objects
 - any time you add a new SCM variable to a struct,
   you need to modify that object type's mark function!

Adding a new type?
 - be sure to call init_TYPE from scwm.c -- search for init_

Using gh_list?
 - terminate the list with SCM_UNDEFINED, not SCM_EOL

Dieing in malloc()?
 - free-d an already freed pointer; consider setting
   the pointer to NULL immediately after freeing it

Be sure not to use, e.g., menu_p() as a C boolean -- use MENU_P() instead
  - the object_p() functions return SCM_BOOL_F or SCM_BOOL_T both of which
    evaluate as true in a C expression. This is also true for the gh_foo_p()
    functions such as gh_string_p and gh_number_p

Creating a scm-level variable with SCWM_VAR_INIT?
  Be sure to initialize with a scheme and not a C value! e.g,.
    SCWM_VAR_INIT(scroll_region, "scroll-region", gh_int2scm(2));


When type checking, consider using, e.g., FONT_OR_SYMBOL_P to permit
  using a symbol when the value is actually used.  Then when you want the
  font, use DYNAMIC_SAFE_FONT(scmFont) to get at the value;
  also see DEREF_IF_SYMBOL for an abstraction for getting the value of
  a symbol.  See also DYNAMIC_PROCEDURE_P and PROCEDURE_OR_SYMBOL_P

Rogue pointer warning?
  - are you marking something that is not an SCM?
    -> scm_gc_mark will not complain if passed an integer type
       because 'typedef long SCM' still

Never return SCM_UNDEFINED -- either return SCM_BOOL_F, or SCM_UNSPECIFIED