scm: mercurial: use to_s for revision in find_changeset_by_name method
On Rails 3.0.11, functional test fails.
<pre> Error: test_diff_two_revs(RepositoriesMercurialControllerTest) NoMethodError: undefined method `empty?' for 4:Fixnum app/models/repository/mercurial.rb:76:in `find_changeset_by_name' </pre>
Authored by: tmaruyama 2012-02-23
Parent: [r8937]
Child: [r8939]
