Checks if this.domain is in fact a Node.JS domain since SimpleWorkflow commonly has a member variable named 'domain' in
context.
More domain calls which need typechecking
make unit tests happy
Merge branch 'master' of github.com:cjhanks/aws-sdk-js into swfDomain
Have renamed this.domain --> this._domain so SimpleWorkFlow will still support domain members.
Fix incompatibility between SWF and domain support

Closes #88