Add support for Hugs's :browse (or :b) command.  There are two forms:

	- :b M   (interpreted modules only) shows everything
          defined in M - the types of top-level functions,
	  and definitions of classes and datatypes.

	- :b *M  shows everything exported from module M.
	  Available for both compiled and interpreted modules.

The user interface is subject to change, but for now it is consistent
with the new semantics of the :module command.

The implementation is a little tricky, since for a package module we
have to be sure to slurp in all the required declarations first.