Fix failing tests, make the onerror and onload tests more comprehensive, remove broken onload function call.
Merge pull request #320 from blakeembrey/duplicate-onload

Fix duplicate onload function calls
Add additional stack trace information to wrappedMethod errors
Added (loose) test case for wrapMethod originating stack traces
Merge pull request #321 from keithamus/showOriginallyWrappedStackTrace

Add additional stack trace information to wrappedMethod errors
Added  to allow iteration of invocations
Merge pull request #322 from jonnyreeves/spy-calls

Added `spy.getCalls()` to allow iteration of invocations