Update Perl to 5.18.4, fix gcc 4.9 build issue

perl r20141002.0 changes:
* support for 5.18.4 (just released)
* download via https / sha1sum of download (https://github.com/Perl/docker-perl/issues/4)
* Fixed failing tests in 5.18 (https://github.com/Perl/docker-perl/issues/5)