The fsync() function takes a Perl file handle as its only argument,
and passes its fileno() to the C function fsync(). It returns undef
on failure, or true on success.

The fsync_fd() function is used internally by fsync(); it takes a
file descriptor as its only argument.

The sync() function is identical to the C function sync().

This module does not export any methods by default, but fsync() is
made available as a method of the FileHandle and IO::Handle classes.
