Commits for RavenDB-1358, RavenDB-1370, RavenDB-1310 and RavenDB-1536

- RavenDB-1358 Missing JavaScript Date.toISOString()
- RavenDB-1370 Backup should give some idea of how far we are from it to finish (minus the Silverlight changes)
- RavenDB-1310 Add LazyCount() option
- RavenDB-1536 Fix Jint Date constructor (linked to RavenDB-1358)

Sorry for sending them all in 1 pull request, I'll do 1 pull request per issue in the future.