innobase/include/srv0srv.h:
  Add configuration variable srv_auto_extend_increment
innobase/srv/srv0srv.c:
  Add configuration variable srv_auto_extend_increment
sql/ha_innodb.h:
  Add configuration variable srv_auto_extend_increment
sql/mysqld.cc:
  Add startup option innodb_autoextend_increment
sql/set_var.cc:
  Add settable global variable innodb_autoextend_increment