add try/catch to async extension init to fix #4404
handle more extension load error cases. add new unit tests.
rename init to initExtension
code review comments
fix jshint error for jasmine globals
Merge pull request #4405 from adobe/jasonsanjose/issue-4404

Rename auto-called extension init method to avoid collisions (fixing #4404).  Add try/catch to async extension init for robustness.