Permit expiration time for doDynamic to be customized rather than being one day.
Appropriate for Jenkins.adjuncts, constructed with a rootURL="adjuncts/${SESSION_HASH}".
Compare 365-day expiration time for /static/* served by Stapler.
Merge pull request #12 from stapler/AdjunctManager.expiration

Permit expiration time for doDynamic to be customized