Issue #1272 - SSP refuses to use temp dir if it doesn't own it, even though it can write to it (#1314)

* Issue #1272 - SSP refuses to use temp dir if it doesn't own it, even though it can write to it
This has been addressed using the is_writable function instead of checking for UID, which only works in a Linux environment

Co-authored-by: Aaron St. Clair <astclair@ecrs.com>