Breakpoints

Hi Pepe,

I played around with breakpoints a little today, they seem to work pretty well - 
nice going!  I discovered a few minor issues that you might be able to clear up:

   - I can't seem to set a breakpoint on 'main'.  In fact, in a file that
     contains only 'main', I get:

*Main> :break add Main 1
*** Exception: Module main:Main was not loaded under debugging mode. Enable 
debugging mode and reload it

     even though I have -fdebugging turned on.

   - we should really let you say ':break add M.f' to add a breakpoint to
     a top-level binding.  It shouldn't be too hard to do this.

   - when GHCi stops at a breakpoint, it should announce the fact, eg.
     "stopped at breakpoint N, module M, M.hs:38:20"

   - really minor one: the help text for :sprint goes over 80 columns

Cheers,
	Simon