This module makes some new features of the Perl 5.14.0 C API available to
XS modules running on older versions of Perl. The features are centered
around the function cv_set_call_checker, which allows XS code to attach a
magical annotation to a Perl subroutine, resulting in resolvable calls to
that subroutine being mutated at compile time by arbitrary C code. This
module makes cv_set_call_checker and several supporting functions
available. (It is possible to achieve the effect of cv_set_call_checker
from XS code on much earlier Perl versions, but it is painful to achieve
without the centralized facility.)
