innobase/include/srv0srv.h:
  Add srv_auto_extend_increment and make SRV_AUTO_EXTEND_INCREMENT
  configureable by it
innobase/srv/srv0srv.c:
  Add srv_auto_extend_increment
sql/ha_innodb.cc:
  Add innobase_auto_extend_increment and srv_auto_extend_increment
sql/ha_innodb.h:
  Add innobase_auto_extend_increment
sql/mysqld.cc:
  Add "innodb_autoextend_increment" configuration option