see /usr/ports/www/apache22/Makefile

CONFLICTS=apache+mod_ssl-1.* apache+mod_ssl+ipv6-1.* apache+mod_ssl+modsnmp-1.* \
         apache+mod_ssl+mod_snmp+ipv6-1.* apache+mod_ssl+mod_accel-1.* \
         apache+mod_ssl+mod_snmp+mod_accel-1.* \
         apache+ipv6-1.* apache+ssl-1.* apache-1.* apache_fp-1.* \
         caudium-devel-1.* caudium10-1.* caudium12-* \
         ru-apache+mod_ssl-1.* ru-apache-1.* thttpd-2.* \
         apache-2.0.* apache-*-2.0.* apache-2.1.* apache-*-2.1.*