Make diffs processing more robust

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.0.5 GA
• Fix Version/s: --Sprint - SP, 6.1.0 CE RC1
• Component/s: Knowledge Base widget
• Labels: None
• Branch Version/s:
  6.0.x, 5.2.x
• Backported to Branch:
  Committed

Used an html parser, rather than directly modifying the raw html.