If soap.wsdl_cache_enabled is on, this setting
determines the type of caching. It can be any of:
WSDL_CACHE_NONE (0),
WSDL_CACHE_DISK (1),
WSDL_CACHE_MEMORY (2) or
WSDL_CACHE_BOTH (3). This can
also be set via the options array in the
SoapClient or SoapServer
constructor.