LU-1812 fsfilt: ext_pblock renamed to ext4_ext_pblock

LU-1812 fsfilt: ext_pblock renamed to ext4_ext_pblock

For kernels 2.6.35 and above ext_pblock was renamed to
ext4_ext_pblock. With no more RHEL5 kernel support for
ldiskfs we also clean up more macros.

see kernel commit bf89d16f6ef5389f1b9d8046e838ec87b9b3f8b9
for pblock change.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Signed-off-by: chas williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Change-Id: I3ce7f27f6fd6826380e6f2f54b2d50d09d36f78a
Reviewed-on: http://review.whamcloud.com/5001
Tested-by: Hudson
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>