[cvs-nhc98] patch applied (hat): Fix several serious bugs in the import mechanism.

[Malcolm Wallace]

Thu Oct  4 07:10:55 PDT 2001  malcolm
  * Fix several serious bugs in the import mechanism.
  
    A module A which imported another module B both qualified and
    unqualified got very confused about what names were visible, and what
    could be re-exported.  The reason was that the qualified/unqualified
    distinction was being applied per module, not per identifier.
  
    A module containing imports such as
        import B (y)
        import B hiding (x)
    was being rejected with the spurious error that using both explicit
    imports and explicit hidings is not permitted.
  
    An implicit
        import qualified Prelude
    was being (incorrectly) added to all modules.
  
  Some bugs still remain for now: it is not possible to import or
  export only some constructors of a type / fields of a type / methods
  of a class.  Either you get all of them or none of them.

    M ./src/compiler98/IExtract.hs -99 +134
    M ./src/compiler98/Import.hs -4 +4
    M ./src/compiler98/Main.hs -2 +2
    M ./src/compiler98/MainNew.hs -9 +8
    M ./src/compiler98/Need.hs -17 +20
    M ./src/compiler98/PreImport.hs -292 +258
    M ./src/compiler98/Rename.hs -8 +8
    M ./src/compiler98/RenameLib.hs -3 +3