fix version in AM.pm
update function calls for PERL_NO_GET_CONTEXT

Following directions in perlguts
(http://perldoc.perl.org/perlguts.html#How-do-I-use-all-this-in-extensions%3f)
update AM.xs to properly pass around the interpreter context on
multi-threaded Perls. This is required because of the addition of
`#define PERL_NO_GET_CONTEXT` in 5313ef8ed74. AM.xs now compiles
without error now.