install capybara on only Ruby 1.9.3 or higher (#12822)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11806 e93f8b46-1217-0410-a6f0-8f06a7374b81
fix failure of test_remove_issue_watcher_from_sidebar at UI IssuesTest

<pre>
  2) Failure:
test_remove_issue_watcher_from_sidebar(Redmine::UiTest::IssuesTest) [test/ui/issues_test.rb:186]:
"Watcher.count" didn't change by -1.
<3> expected but was
<4>.
</pre>

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11807 e93f8b46-1217-0410-a6f0-8f06a7374b81
prevent assert_difference failure of test_watch_issue_via_context_menu at UI IssuesTest

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11808 e93f8b46-1217-0410-a6f0-8f06a7374b81
prevent assert_difference failure of test_bulk_watch_issues_via_context_menu at UI IssuesTest

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11809 e93f8b46-1217-0410-a6f0-8f06a7374b81
run test:ui on CI Server Ruby 1.9.3 or higher (#12822)

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11810 e93f8b46-1217-0410-a6f0-8f06a7374b81