Converted the REDMINE_SUPPORTED_SCM constant to a class

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

app/views/settings/_repositories.rhtml

@@ -13,7 +13,7 @@
   <%= link_to_function l(:label_generate_key), "if ($('settings_sys_api_key').disabled == false) { $('settings_sys_api_key').value = randomKey(20) }" %>
 </p>
 
-<p><%= setting_multiselect(:enabled_scm, REDMINE_SUPPORTED_SCM) %></p>
+<p><%= setting_multiselect(:enabled_scm, Redmine::Scm::Base.all) %></p>
 
 <p><%= setting_text_field :repositories_encodings, :size => 60 %><br />
 <em><%= l(:text_comma_separated) %></em></p>