Re #274: Crash when missing unit member ID * Add key and keyref for member type Re #290: Migrate to using key/keyref definitions instead of ID/IDREF type * Move keyref and key for equipment slot to correct place to be valid * Add aliased xmlns for schema to allow for use in XPath, which doesn't use default namespace * Disable warning reporting until Mono Bug 613684 is fixed (https://bugzilla.novell.com/show_bug.cgi?id=613684)