Fix traceback on revision compare with bad params

* Catch exceptions in parsing to/from revision parameters

* Re-enable CompareRevisionTests, with a couple of fixes

* Added test_bad_parameters
Merge pull request #871 from lmorchard/fix-revision-param-error

Fix traceback on revision compare with bad params
fix bug 809523: API access to document summary

* ?summary option on document URLs to serve just the summary (combines
  with ?raw & etc)

* $children doc view now includes summaries, for page.subpages in
  kumascript

* $json doc vies now includes summary, for wiki.getPage in kumascript

* Added option to get_seo_summary to strip / not strip markup

* get_seo_summary will now first look for a "Summary" section
Merge pull request #872 from lmorchard/809523-page-summary-api

fix bug 809523: API access to document summary
fix bug 841427 - Allow 'Launch' link context item
Merge pull request #873 from darkwing/launch-link-841427

fix bug 841427 - Allow 'Launch' link context item
Add label for usability improvement
Merge pull request #874 from darkwing/label-newsletter

Add label for usability improvement
bug 839341: Properly delete demo files when submission record deleted
Fix bug 842815: Update 404 page with form.doc link
Fix bug 842825: Update Bugzilla links to form.mdn
Merge pull request #876 from openjck/form.mdn-links

Fix bug 842825: Update Bugzilla links to form.mdn
Merge pull request #877 from openjck/404-form.doc

Fix bug 842815: Update 404 page with form.doc link
Merge pull request #875 from lmorchard/839341-demo-files-removed-on-delete

bug 839341: Properly delete demo files when submission record deleted
fix bug 843078 - Update build timestampfor CKEditor
Merge pull request #878 from darkwing/ckeditor-cdn-843078

fix bug 843078 - Update build timestampfor CKEditor
Don't return null item redirects from children view
Merge pull request #879 from darkwing/children-redirects

Don't return null item redirects from children view
fix bug 821255 - retry basket for transient errors
Merge pull request #882 from groovecoder/newsletter-exceptions-821255

fix bug 821255 - retry basket for transient errors