Rewrote inline discussions hotfix from 58553a7f

In general, this is a very straight forward fix - I decided not to
cherry-pick directly from 58553a7f
as the diff exposes very radical differences.

common/static/coffee/src/discussion/views/discussion_thread_view_inline.coffee

@@ -45,7 +45,7 @@ if Backbone?
 
     expandPost: (event) =>
       @$el.addClass('expanded')
-      @$el.find('.post-body').html(@model.get('body'))
+      @$el.find('.post-body').text(@model.get('body'))
       @showView.convertMath()
       @$el.find('.expand-post').css('display', 'none')
       @$el.find('.collapse-post').css('display', 'block')
@@ -60,7 +60,7 @@ if Backbone?
       if postTop < curScroll
         $('html, body').animate({scrollTop: postTop})
       @$el.removeClass('expanded')
-      @$el.find('.post-body').html(@model.get('abbreviatedBody'))
+      @$el.find('.post-body').text(@model.get('abbreviatedBody'))
       @showView.convertMath()
       @$el.find('.expand-post').css('display', 'block')
       @$el.find('.collapse-post').css('display', 'none')