Add "Disable Local Display" option for doors, parse DOSXTRN.ERR

New option to disable local screen display for door programs: sets the 'Screen' value appropriately in door.sys or pcboard.sys drop files and on Windows, doesn't create a new console window.

Also, now parsing the DOSXTRN.ERR file created by the latest/greatest dosxtrn.exe when failing to execute the child/DOS program and log the parsed error details (errno value and description), helpful in debugging the reason why a DOS program may not have been successfully executed by DOSXTRN.