Merge branch 'master' of github.com:simplesamlphp/simplesamlphp

# By Thijs Kinkhorst
# Via Jaime Pérez (1) and Thijs Kinkhorst (1)
* 'master' of github.com:simplesamlphp/simplesamlphp:
  composer: replace xmlseclibs svn source with our git copy