Building with RHEL6.2 beta (kernel-2.6.32-204) exposed that the
HAVE_STATFS_DENTRY_PARAM autoconf check was incorrect. The test
was setup to check the first argument of vfs_statfs() function.
However, the conditional code itself doesn't use the vfs_statfs()
function it registers a function with the sops->statfs() callback.

Historically, this always worked because both of these prototypes
were changed in a single upstream kernel commit (726c3342). However,
as of RHEL6.2 the vfs_statfs() function changed again and the
sops->statfs() callback stayed the same. The vfs_statfs() function
now takes a path structure as the first parameter.

This was fixed by simply updating the autoconf test to check the
prototype of the function were going to actually use.