ZF-3547: Allow persistent connections in Zend_Http_Client_Adapter_Socket

Description

Allow Zend_Http_Client_Adapter_Socket to use persistent TCP connections through a configuration option (set to off by default)

Comments

Fixed in rev. 9868 including documentation and unit tests.

\In order to use, the ('persistent' => true) configuration flag must be passed.

Does not break BC.

Updating for the 1.6.0 release.