Add subselect to query builder
Fix many to many polymorphic pivot updates

`$morphType ` set by `setMorphType` is being included in queries from x->pivot->save() and the like. As the object is being added as a public data member on an object with an empty original, it is treated as an attribute and added as a column to the queries. As this column doesn't exist, the query will be erroneous.

https://github.com/laravel/framework/issues/3693
Merge pull request #4288 from skovacs1/4.1

[Bug] Fix many to many polymorphic pivot updates
Add note.
Merge branch '4.1' into 4.2
Merge branch '4.2'
Add updateOrCreate() function
Merge pull request #4201 from alprs/feature/query-subselect

Add subselect to query builder
Cleaning up code.
Merge pull request #4602 from lucasmichot/4.2-model-updateorcreate

[4.2] Add updateOrCreate() function
Spacing.
Update change log.
Merge branch '4.2'