Ticket 408 - Fix crash when disabling/enabling the setting

Bug Description:  Enabling/disabling can lead to crash as the setting
                  was not designed to be dynamically updated.

Fix Description:  Do not use the actual config setting to determine if the
                  cache is enabled.  Instead we record when the cache is
                  initialized.  The server still needs to be restarted for
                  the config change to take effect.

                  Also freed the cache at server shtudown.

https://fedorahosted.org/389/ticket/408

Reviewed by: rmeggins(Thanks!)
(cherry picked from commit 03c90f04065059ee310e9fa7d98228e0aa39fa50)
(cherry picked from commit 50ad64a442495810a84558c6c17dcc2263b815b6)
(cherry picked from commit e0d85bead832c6aa7a2ec01157ab786a53fb5272)
Ticket #47516 replication stops with excessive clock skew

https://fedorahosted.org/389/ticket/47516
Reviewed by: nhosoi (Thanks!)
Branch: 389-ds-base-1.3.1
Fix Description: The previous fix was not adequate.  Instead, the determination
of whether or not to ignore time skew should be determined in
csngen_adjust_time().
Platforms tested: RHEL6 x86_64
Flag Day: no
Doc impact: yes - document new config param
(cherry picked from commit 9f2b104b0938b21d7c9fe37c736d0e6328843aeb)
(cherry picked from commit a6ec074c6295a59938f313b4fe09430e8f601fab)