Bump VERSION, update CHANGELOG and release.

CHANGELOG

@@ -1,4 +1,4 @@
-v0.6.4 (2011-??-??)
+v0.6.4 (2011-02-12)
   * Various performance improvements (15% ~ 25%) especially when dealing with 
     long multibulk replies or when using clustered connections.
 

VERSION

@@ -1 +1 @@
-0.6.4-dev
+0.6.4