Detect broken system linux/fiemap.h

Detect broken system linux/fiemap.h

RedHat 5.5 has a /usr/include/linux/fiemap.h, but it is
broken because it does not itself include linux/types.h.
As a result, __u64 and friends are not defined.

We have a Ceph-local copy of fiemap.h, so use it
if the system version is broken.

While we're at it, fix up the configure message to
note we're using a local copy.

Signed-off-by: Jim Schutt <jaschut@sandia.gov>
Signed-off-by: Sage Weil <sage@newdream.net>