MFC r305916,r305918:

r305916:

Make sure $TMPDIR is created with 0755 permissions

This is required to ensure that the temporary script can be executed,
as the default mode is apparently too restrictive

r305918:

Only chmod $TMPDIR if it's not /tmp

This is a safety belt to ensure that the /tmp sticky bit stuff doesn't
get whacked by accident if someone runs the script outright