[BUGFIX] Only set pending ajax requests if they are falsy

Conflicts:
	packages/ember-testing/tests/helpers_test.js
Update enumerable_utils.js

-It should be 'removed' not 'remove'
-'modified' sounds better than 'changed'
[DOC] Improve register/inject documentation
[DOC] Correction for `ActionHandler` implementing classes
Minor fix for to detect `find` method

Fixes #4583

Conflicts:
	packages/ember-routing/tests/system/route_test.js
[BUGFIX beta] #4474 - Assertion when using 'basic' as a route or resource name.

[BUGFIX beta] #4474 - Assertion when using 'basic' as a route or resource name.

Foo

Foo