Now SCMs can be added or removed using a simple API, instead of being
hardcoded:

  Redmine::Scm::Base.add('ScmName')
  Redmine::Scm::Base.delete('ScmName')

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3440 e93f8b46-1217-0410-a6f0-8f06a7374b81