a major refactoring in the C and the Haskell runtimes. Note incompatible change in the PGF format!!!

The following are the outcomes:

   - Predef.nonExist is fully supported by both the Haskell and the C runtimes

   - Predef.BIND is now an internal compiler defined token. For now
     it behaves just as usual for the Haskell runtime, i.e. it generates &+.
     However, the special treatment will let us to handle it properly in 
     the C runtime.

   - This required a major change in the PGF format since both 
     nonExist and BIND may appear inside 'pre' and this was not supported
     before.

src/runtime/haskell/PGF/Data.hs

@@ -58,9 +58,10 @@ data Symbol
   = SymCat {-# UNPACK #-} !Int {-# UNPACK #-} !LIndex
   | SymLit {-# UNPACK #-} !Int {-# UNPACK #-} !LIndex
   | SymVar {-# UNPACK #-} !Int {-# UNPACK #-} !Int
-  | SymKS [Token]
-  | SymKP [Token] [Alternative]
+  | SymKS Token
   | SymNE                           -- non exist
+  | SymBIND                         -- the special BIND token
+  | SymKP [Symbol] [([Symbol],[String])]
   deriving (Eq,Ord,Show)
 data Production
   = PApply  {-# UNPACK #-} !FunId [PArg]
@@ -75,10 +76,6 @@ type FunId = Int
 type SeqId = Int
 type BCAddr = Int
 
-data Alternative =
-   Alt [Token] [String]
-  deriving (Eq,Ord,Show)
-
 
 -- merge two PGFs; fails is differens absnames; priority to second arg