shlib.sh: stop using non-portable mktemp -t option
The mktemp -t option does different things on different
platforms. The intention being that the resulting file
gets created in the appropriate "temporary" directory.
In actuality, mktemp just looks at the TMPDIR environment
variable and defaults to /tmp if it's not set (at least
that's the wanted behavior).
Stop using the -t option and simply prefix the template
with ${TMPDIR:-/tmp}/ instead (or a reasonable but
slightly safer facsimile thereof).
Signed-off-by: Kyle J. McKay <mackyle@gmail.com>