BUG #4965: missing tests in tools/fsync/test_fsync.c

The following bug has been logged online:

Bug reference: 4965
Logged by: Jeff Janes
Email address: jeff(dot)janes(at)gmail(dot)com
PostgreSQL version: 8.4.0
Operating system: Linux
Description: missing tests in tools/fsync/test_fsync.c
Details:

In the part that implements "Compare file sync methods with one 8k write",
the #ifdef OPEN_SYNC_FLAG code
is nested within the #ifdef OPEN_DATASYNC_FLAG code.

This causes o_sync to be skipped if o_dsync is unavailable, but only for
this particular section (the section with 2 8k writes doesn't have this
problem.)

Also, the statement that prints the "Compare file sync methods with one 8k
write" section title is up in the #ifdef block of a previous section, where
it might be omitted on systems without an o_sync.