Hook igbinary into APC serializer hooks

Hook igbinary into apc's new serializer hooks

http://svn.php.net/viewvc/pecl/apc/trunk/apc_serializer.h?revision=HEAD&view=markup

The patch detects apc-devel headers on build and adds in apc serializer support, but there is no
direct linking or symbolic dependencies, so both packages can be used independently of the
other, even after a build with support.