There are three functions in here:

* addressOf: Extremely useful when debugging a gjs process with a
  native code debugger like GDB.  Add "print(imports.system.addressOf(foo))"
  for an object, then take the number it prints "12345" and paste into
  gdb like:
  p (JSObject*) 12345
* breakpoint: Wrapper for G_BREAKPOINT().  Insert a SIGTRAP which,
  if the process is under a debugger, causes a breakpoint.  Combines
  nicely with the above.
* gc: Forces a full garbage collection.