a partial support for def rules in the C runtime

The def rules are now compiled to byte code by the compiler and then to
native code by the JIT compiler in the runtime. Not all constructions
are implemented yet. The partial implementation is now in the repository
but it is not activated by default since this requires changes in the
PGF format. I will enable it only after it is complete.

src/compiler/GF/Text/Coding.hs

@@ -23,7 +23,7 @@ encodeUnicode enc s =
   where
     translate cod cbuf
       | i < w     = do bbuf <- newByteBuffer 128 WriteBuffer
-                       (_,cbuf,bbuf) <- cod cbuf bbuf
+                       (cbuf,bbuf) <- cod cbuf bbuf
                        if isEmptyBuffer bbuf
                          then ioe_invalidCharacter1
                          else do let bs = PS (bufRaw bbuf) (bufL bbuf) (bufR bbuf-bufL bbuf)
@@ -48,7 +48,7 @@ decodeUnicodeIO enc (PS fptr l len) = do
   where
     translate cod bbuf cbuf
       | i < w     = do
-                       (_,bbuf,cbuf) <- cod bbuf cbuf
+                       (bbuf,cbuf) <- cod bbuf cbuf
                        if isEmptyBuffer cbuf
                          then ioe_invalidCharacter2
                          else unpack cod bbuf cbuf