Incorrect overall status when failing to save a tracked reference

If there is an error in the child tracking task, it is handled properly.

If on the other hand tracking completes successfully, and we fail to rewrite the file on disk (can be reproduced by removing write permission from the .bst file and it's parent directory), then we just print a message telling the user that we failed.

What we fail to do (and this applies to any failure in a Queue implementation in the main process):

Report overall failure state message (last log line still says SUCCESS)
Report the appropriate -1 exit code (automated scripts cannot check for this kind of failure)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information