change the encoding of uints to simplify overflow checking and to make them

easier and faster to read.  they are now either a one-byte value or a n-byte value
preceded by a byte holding -n.

R=rsc
DELTA=150  (45 added, 7 deleted, 98 changed)
OCL=32381
CL=32387

src/pkg/gob/encoder_test.go

@@ -50,8 +50,7 @@ func TestBasicEncoder(t *testing.T) {
 	}
 
 	// Decode the result by hand to verify;
-	state := new(decodeState);
-	state.b = b;
+	state := newDecodeState(b);
 	// The output should be:
 	// 0) The length, 38.
 	length := decodeUint(state);