configure.in	Check if fdatasync exists
manual.texi	Updated defragmenting doc
manual.texi	Corrected fillfactor contract threashold for a page to 1/2


Docs/manual.texi:
  Updated defragmenting doc
innobase/configure.in:
  Check if fdatasync exists
innobase/os/os0file.c:
  Use O_SYNC if possible, second choice fdatasync, and last choice fsync