Let Bootstrap's tab JS handle history

Closes #2219

app/assets/javascripts/merge_request.js.coffee

@@ -58,14 +58,6 @@ class @MergeRequest
       , 'json'
   bindEvents: ->
-    this.$('.merge-request-tabs').on 'click', 'a', (event) =>
-      a = $(event.currentTarget)
-
-      href = a.attr('href')
-      History.replaceState {path: href}, document.title, href
-
-      event.preventDefault()
-
     this.$('.merge-request-tabs').on 'click', 'li', (event) =>
       this.activateTab($(event.currentTarget).data('action'))

app/views/projects/merge_requests/_show.html.haml

@@ -36,17 +36,17 @@
   - if @commits.present?
     %ul.nav.nav-tabs.merge-request-tabs
-      %li.notes-tab{data: {action: 'notes'}}
+      %li.notes-tab{data: {action: 'notes', toggle: 'tab'}}
         = link_to merge_request_path(@merge_request) do
           %i.fa.fa-comments
           Discussion
           %span.badge= @merge_request.mr_and_commit_notes.user.count
-      %li.commits-tab{data: {action: 'commits'}}
+      %li.commits-tab{data: {action: 'commits', toggle: 'tab'}}
         = link_to merge_request_path(@merge_request), title: 'Commits' do
           %i.fa.fa-history
           Commits
           %span.badge= @commits.size
-      %li.diffs-tab{data: {action: 'diffs'}}
+      %li.diffs-tab{data: {action: 'diffs', toggle: 'tab'}}
         = link_to diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request) do
           %i.fa.fa-list-alt
           Changes