update 0.971a

- Fixed a pretty bad mistake that caused the checker to have 100% CPU
usage at all times
- credits.txt should no longer be getting parsed as txt layout file
- shipBlueprints should now recognize "random" and "ghost" as correct
- the checker now always opens files in read-only mode, and therefore
should not ever require the user to run it as admin
- hostile= attribute in ship events is no longer mandatory
- objects linked from inside of ship events should now be correctly
considered used by the checker
- fixed the checker crashing when an error occured during parsing that
would cause the XML document to not be created