Initial import of p5-GSSAPI 0.21

Initial import of p5-GSSAPI 0.21

Gives access to the routines of the GSSAPI library, as described in
rfc2743 and rfc2744 and implemented by the Kerberos-1.2 distribution
from MIT.
Since 0.14 it also compiles and works with Heimdal. Lacks of Heimdal
support are gss_release_oid(), gss_str_to_oid() and fail of some tests.
The API presented by this module is a mildly object oriented
reinterpretation of the C API, where opaque C structures are Perl
objects, but the style of function call has been left mostly untouched.
As a result, most routines modify one or more of the parameters passed
to them, reflecting the C call-by-reference (or call-by-value-return)
semantics.
All users of this module are therefore strongly advised to localize all
usage of these routines to minimize pain if and when the API changes.