scm: mercurial: change two revision diff text of mercurial (#3724).

For example, "4:def6d2f1254a 2:400bb8672109".

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4699 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/repository/mercurial.rb

@@ -42,6 +42,10 @@ class Repository::Mercurial < Repository
     changeset.scmid
   end
 
+  def diff_format_revisions(cs, cs_to, sep=':')
+    super(cs, cs_to, ' ')
+  end
+
   def entries(path=nil, identifier=nil)
     entries=scm.entries(path, identifier)
     if entries