Document recent MediaWiki vulnerabilities

Security: CVE-2015-8628
Security: CVE-2015-8627
Security: CVE-2015-8626
Security: CVE-2015-8625
Security: CVE-2015-8624
Security: CVE-2015-8623
Security: CVE-2015-8622
Security: https://vuxml.FreeBSD.org/freebsd/f36bbd66-aa44-11e5-8f5c-002590263bf5.html