* rdebug.el is loaded by the user when Emacs is launched. (Should
Rdebug ever be part of Emacs, this should be the items autoloaded by
Emacs.)

There is a command buffer which is the gud process. There are a number
of "secondary" buffers have in gud-comint-buffer the gud process. The
way we go the other direction from gud process to secondary buffer is
by buffer name. Source buffers don't seem to have a local
gud-comint-buffer variable set but use the global value. Perhaps
source buffer should have their own buffer-local value(s)?

For each secondary buffer we have things for that specific buffer. In particular:
* frames (rdebug-frames.el)
* output (rdebug-output.el)
* variables (rdebug-varbuf.el)
* watch or display-expressions - (rdebug-watch.el
* breakpoints (rdebug-breaks.el)

Each specific secondary buffer includes 
 - setting the buffer up,
 - specific commands for that buffer 
 - the kinds of functions that buffer deals with (e.g. frame
   things for the "frame" buffer or breakpoints for the "breakpoints" buffer.)

* rdebug-gud.el contains things that interface to gdb. Possibly also
things that interface to gdb-ui should be there as well.

* rdebug-shortkey.el has all the magic that needs to be done to make
  shortkey mode work. 

* rdebug-track is all the things to make rdebug-track mode work.

I have some additions, which deals with *when* certain files are loaded.

* rdebug-source.el is loaded when the first Ruby source file is loaded
Of course, the name rdebug-source.el is not important, we could rename
it to something else and reuse the name for other source-related
things.
