Improve .isDefined()

 On branch master

	modified:   index.js
Test possible key collisions.

 On branch master

	modified:   test/test.js
Protect private reference pointer.

 On branch master

	modified:   index.js
	modified:   test/test.js
Simplify constant definition.

 On branch master

	modified:   index.js
isssue #1 Deep freeze with .freeze()

 On branch master

	modified:   index.js
	modified:   test/test.js