use TMPDIR if set

updated tmpnam to use TMPDIR if it is set.

This was provoked via an email I received from a colleague at my previous university.

Taylor,

I’m not sure how to submit suggestions for code updates to the FSL group.

On our Hyperion supercomputing cluster, the /tmp area on each node is limited to 2GB, and of course that is shared with other users running jobs on the same node. This has caused FSL to fail on Hyperion when there was not enough free disk space available.

My suggested change is to have the tmpnam command examine the TMPDIR environment variable, and use that if is available. If it not set, the code functions precisely as it did previously.

Please see the attached code. I welcome any comments or suggestions you might have.

Thanks,

David Paul Reddy Research Scientist he/him/his