make 6g constants behave as ken proposes.  (i hope.)
various bug fixes and tests involving constants.

test/const1.go is the major new test case.

R=ken
OCL=26216
CL=26224
diff --git a/test/const2.go b/test/const2.go
new file mode 100644
index 0000000..b3b10de
--- /dev/null
+++ b/test/const2.go
@@ -0,0 +1,12 @@
+// errchk $G $D/$F.go
+
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+const (
+	A int = 1;
+	B byte;	// ERROR "type without expr"
+)