how to use ghci-debugger with packages

[Simon Marlow]

Frederik Eaton wrote:

> P.S. Here are some suggestions for the GHCi debugger documentation:
> 
> http://www.haskell.org/ghc/dist/current/docs/users_guide/ghci-debugger.html
> 
> "There is one major restriction: breakpoints and single-stepping are only available in interpreted modules; compiled code is invisible to the debugger."
> -->
> "There is one major restriction: breakpoints and single-stepping are only available in interpreted modules; compiled code is invisible to the debugger. Note that packages only contain compiled code - so debugging a package requires finding its source and loading that directly."
> 
> "There is currently no support for obtaining a "stack trace", but the tracing and history features provide a useful second-best, which will often be enough to establish the context of an error."
> -->
> "There is currently no support for obtaining a "stack trace", but the tracing and history features provide a useful second-best, which will often be enough to establish the context of an error. For instance, it is possible to break automatically when an exception is thrown, even if it is thrown from within compiled code (see 3.5.6. Debugging exceptions)."

Thanks!  I'll push these changes.

Cheers,
	Simon