Don't initialize Tree History unless tree-slider is present

This was breaking breadcrumb links on non-Tree pages

app/assets/javascripts/tree.js.coffee

@@ -18,7 +18,6 @@ $ ->
       "ajax:complete":   -> $('.tree_progress').removeClass("loading")
 
     # Maintain forward/back history while browsing the file tree
-
     ((window) ->
       History = window.History
       $ = window.jQuery
@@ -28,7 +27,6 @@ $ ->
       unless History.enabled
         return false
 
-  $ ->
       $('#tree-slider .tree-item-file-name a, .breadcrumb li > a').live 'click', (e) ->
         History.pushState(null, null, $(@).attr('href'))
         return false