This module supports some of the new features of the Perl 5.14.0 C API running the XS module
on older versions of Perl, it is available using cv_set_call_checker and several support
functions. (On earlier versions of Perl, you could implement the cv_set_call_checker effect
from the XS code. But without centralized facilities, it can be painful.)
The features revolve around the function cv_set_call_checker, which allows XS code to attach
a magical comment to a Perl subroutine, resulting in resolvable calls to that subroutine that
can be modified by C code at compile time.
