Fix SASL_CB_GETCONF(PATH) detection
Fix SASL_CB_GETCONF(PATH) detection

For https://github.com/memcached/memcached/issues/365 
On RHEL(5|6|7) the name of the defined constant in sasl.h is SASL_CB_GETCONFPATH and not SASL_CB_GETCONF.
This adds support for HAVE_SASL_CB_GETCONFPATH to be set to nonzero when the SASL implementation supports SASL_CB_GETCONFPATH.  This will be used in sasl_defs.c when ./configure is run with "--enable-sasl".
dormando/memcached,memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached,memcached/memcached,memcached/memcached,dormando/memcached,dormando/memcached,memcached/memcached