Have travis generate test coverage using istanbul.
Report coverage to build log and coveralls.
HTTP Out - header properties must be strings
HTTP Out - stringed the wrong bit
Handle null response payloads
Http Out: remove excess debug
HTTP Out payload: relax null checking
Merge pull request #260 from hindessm/test-coverage

Test coverage on coveralls.io
Add more Node tests.
Refactor common log code.
Add test for the null message case.
Short circuit the null message case.