Fix code not to call exit if it can't open a file for writing. This is not

Fix code not to call exit if it can't open a file for writing. This is not
library-friendly. In general, all of the calls to exit() should be reviewed
with an eye to this.

I believe I have altered things correctly in gvRenderJobs so that cleanup is done
correctly and finalizers are called as needed for good jobs. It would be good for
John to review the changes.