AME-4298, CR-4390 - Introduce 'Reduced Crosstalk Purge Delay' configuration variable

The 'Reduced Crosstalk Purge Delay' variable defines the length of time (in minutes) that remote
sessions are retained in the Session.sessionTable in order to avoid a stale read from CTS allowing
use of a destroyed session from a remote OpenAM server.

git-svn-id: https://svn.forgerock.org/openam/branches/AME-3423@10344 0f4defcf-c51a-4c67-9f44-6fb5eba73c5d