VERSION, params: begin Geth 1.6.4 release cycle

VERSION

@@ -1 +1 @@
-1.6.3
+1.6.4

params/version.go

@@ -21,10 +21,10 @@ import (
 )
 
 const (
-	VersionMajor = 1        // Major version component of the current release
-	VersionMinor = 6        // Minor version component of the current release
-	VersionPatch = 3        // Patch version component of the current release
-	VersionMeta  = "stable" // Version metadata to append to the version string
+	VersionMajor = 1          // Major version component of the current release
+	VersionMinor = 6          // Minor version component of the current release
+	VersionPatch = 4          // Patch version component of the current release
+	VersionMeta  = "unstable" // Version metadata to append to the version string
 )
 
 // Version holds the textual version string.