Add k_haspag to libkopenafs

Add k_haspag to libkopenafs

Add the k_haspag function to libkopenafs, which returns true if the
current process is in a PAG and false otherwise.

The implementation currently duplicates code from the ktc_curpag
function since the latter calls the regular pioctl() interface and
hence introduces an Rx dependency that we're avoiding for libkopenafs.
This should be refactored to avoid the code duplication at some point,
but that will require building a utility library that can be reasonably
linked into libkopenafs and is therefore deferred for future work.

Change-Id: Ib97322ef24dc3a4e48cb45090c516c95b71e9fc7
Reviewed-on: http://gerrit.openafs.org/2041
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>