Allow demongoization of strings to float

[ fix #3089 ]
Remove forgotten remnants of Mongoid::Observer

c.f. mongoid/mongoid#3108
Mention removal of Mongoid::Observer in CHANGELOG
Merge pull request #3289 from herimedia/niels-remove-observers

Remove forgotten remnants of Mongoid::Observer
update changelog
mark as pending a IdentityMap broken test
Use ActiveSupport::Notifications to send operations logs
add log subscriber tests
Minor fixes in comments
Another minor fix in comments
Merge pull request #3295 from Spone/patch-1

Minor fixes in counter_cache comments
Point to moped master on Gemfile for now
Merge pull request #3292 from mongoid/log_subscriber_spec

add log subscriber tests
make storage_options set the default on include
validate self class on store_in
Bump moped to beta2
Return 0 instead of nil on sum with no matches.

[ fix #2678 ]

Conflicts:
	CHANGELOG.md
	spec/mongoid/contextual/aggregable/memory_spec.rb
	spec/mongoid/contextual/aggregable/mongo_spec.rb
Update changelog: add Sample syntax to new session opts
add query counter helper to rspec
Add criteria aliases via alias_attribute.

[ close #3302 ]