Demonstrate polymorphic association + map - discussion #54
Modified to simplify discussion #51
Made test case variable local
always do `set` to existing nested collection : fixes #31
Add an extra type param to the map function
Re-work to remove mapper function to simplify scenario #51. Use option.merge = false instead
Refactor test case to demonstrate use of the new type param
Merge branch 'master' of https://github.com/dhruvaray/backbone-associations

Conflicts:
	backbone-associations.js
Added support for new map itnerface when adding to collections.