data files.  Previously, writes were flushed until the doublewrite
buffer was created.  That would be too slow on systems where
os_file_flush() [or fsync(2)] is slow.  (Bug #12125)


innobase/include/os0file.h:
  Disable os_do_not_call_flush_at_each_write unless #ifdef UNIV_DO_FLUSH
innobase/os/os0file.c:
  Disable os_do_not_call_flush_at_each_write unless #ifdef UNIV_DO_FLUSH
innobase/trx/trx0sys.c:
  Disable os_do_not_call_flush_at_each_write unless #ifdef UNIV_DO_FLUSH