xfstests: don't assume that falloc_punch implies falloc in test 255

xfstests: don't assume that falloc_punch implies falloc in test 255

As of Linux 3.9-rc1, ext4 will support the punch operation on file
systems using indirect blocks, but it can not support the fallocate
operation (since there is no way to mark a block as uninitialized
using indirect block scheme).  This caused test 255 to fail, since it
only used _require_xfS_io_falloc_punch assuming that all file systems
which supported punch can also support fallocate.  Fix this.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>