securid: Avoid time_t overflows

The 14-bit time field in V2 tokens can represent dates beyond Jan 2038,
when 32-bit UNIX times (time_t) overflow.  Tokens that encode such a
date will erroneously show an expiration date in 1908, so we need to
add an explicit cap.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
tests: Use a token that expires in 2038

The original test token expires in Sept 2015, which will cause
"make check" to start failing on its own.  Generate a new test token
with an expiration date in 2038 so this will not be a concern.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>