Fix ShadowParcel.writeString(), add ShadowParcel.writeByteArray() and ShadowParcel.createByteArray().

Fix ShadowParcel.writeString() to accept null as a valid value instead of ignoring it. I verified on Gingerbread and ICS that this is how Android behaves.

Add ShadowParcel.writeByteArray() and ShadowParcel.createByteArray().