Split off serialization and key functions to their own packages.

service/datastore/raw_interface.go

Index: service/datastore/raw_interface.go
diff --git a/service/datastore/raw_interface.go b/service/datastore/raw_interface.go
index a3db860d9587acaff05075cdecc1d557eb664fc7..e9c77c6924433fe29bfaa21dbeaa90a31a62ffbf 100644
--- a/service/datastore/raw_interface.go
+++ b/service/datastore/raw_interface.go
@@ -21,6 +21,23 @@ type Key interface {
 	AppID() string
 	Namespace() string
 
+	// Incomplete returns true iff k doesn't have an id yet.
+	Incomplete() bool
+
+	// Valid determines if a key is valid, according to a couple rules:
+	//   - k is not nil
+	//   - every token of k:
+	//     - (if !allowSpecial) token's kind doesn't start with '__'
+	//     - token's kind and appid are non-blank
+	//     - token is not incomplete
+	//   - all tokens have the same namespace and appid
+	Valid(allowSpecial bool, aid, ns string) bool
+
+	// PartialValid determines if a key is valid for a Put operation. This is
+	// like Valid(false, aid, ns), except that the childmost key is allowed to
+	// be Incomplete().
+	PartialValid(aid, ns string) bool
+
 	String() string
 }