Improved readline command completion support

Hi,

fyi, I wrote a patch that improves the readline command completion
support of hugs.  It is available at
http://hackage.haskell.org/trac/hugs/ticket/61 .

I.e.:
- added completion of function names and constructors 
- added completion of command names (:<cmd>)
- added completion of module names (e.g. after :browse , etc.)
- only do filename completion where it makes sense (e.g. after :load , etc.)
- expand use of tilde (~) in filenames (previously it was completed
  but not recognized by hugs)
- read and write the history from/to ~/.hugs_history
- make hugs recognize :help

Best regards
Georg Sauthoff