xmltooling: several vulnerabilities

Several vulnerabilities have been discovered in the xmltooling packages, as used by Shibboleth:

Chris Ries discovered that decoding a crafted URL leads to a crash (and potentially, arbitrary code execution).

Ian Young discovered that embedded NUL characters in certificate names were not correctly handled, exposing configurations using PKIX trust validation to impersonation attacks.

Incorrect processing of SAML metadata ignores key usage constraints. This minor issue also needs a correction in the opensaml2 packages, which will be provided in an upcoming stable point release (and, before that, via stable-proposed-updates).