Prohibit find() with no selector in Bulk API

RUBY-722
Merge branch '1.x-stable-ruby-722' of https://github.com/gjmurakami-10gen/mongo-ruby-driver into gjmurakami-10gen-1.x-stable-ruby-722
aggregate option for external sort should be "allowDiskUse" rather than "allowDiskUsage"

RUBY-682
RUBY-723 Support the $meta projection operator
RUBY-723 Support the $meta sort field