proposed changes in module search behaviour

[Ross Paterson]

I propose to make two changes to Hugs's module search behaviour:

- remove the A.B.C.hs feature: no-one seems to be using it, GHC doesn't
  do it, and it's doubling the number of files tried.

- don't search the current directory, unless it's explicitly given in
  the path (but put it at the front of the default path to preserve
  the current behaviour).  At least people could then turn it off if
  required.

Note that this relates only to resolving module names -- file names
don't use the path.  Also, when a file name is specified, the directory
containing it is searched first for any modules imported by that file
(and other modules found in that directory).