Reprocess failed ajax request.

When an ajax request fails the client will resend the request.

With this patch, if the failure is caused by the server (http code >500) the retry-request will actually be processed again instead of being satisfied by the previously computed response (which was a failure)
Make sure to satisfy any pending future even if the request failed
JObjectField doesn't serialize to BSON
Removed abstract from JObjectField
* Added comments to LiftRules.onBeginServicing and earlyInStateful
* Fixed a lift-json test that was failing at random.
Make some minor comment improvements to LiftActor.scala.
Make some minor comment improvements to CometActor.scala.
Added CONTRIBUTING.md.
Add title to contribution guidelines.
Update version of joda time, slf4j & logback
Make mapper specs pass even if system locale is da_DK :-)
Upgrade mongo-java-driver to v2.10.1
Adding ajaxEditableSelect to SHtml. Allows users to dynamically add new selections into an ajaxSelect.
don't clobber a user given id attribute
Memoize the value of a resource lookup for the duration of the request.

Closes #1372
Avoid exceptions in default error handler.

The toString method on Req will throw if it contains files that are too
large for the configured limits
Improve error handling in case exceptionHandlers throw.

Now any errors that occurs in exceptionHandlers are ignored (but
logged), instead returning an empty response
Return a real error message & 500 status in case the error processing
fails
Fix parsing when buffer is exhausted
Remove lift-couchdb from framework. It is now a lift module.