Do not export Client in ringo/httpclient, and some minor enhancements.
Do not export Client in ringo/httpclient, and some minor enhancements.

Client instances use private thread pools that can lead to massive
memory leaks if not closed properly.
Other changes include:
   - delay instantiation of Jetty HttpClient until a request is made
   - make Exchange properties enumerable

oberhamsi/ringojs,ashwinrayaprolu1984/ringojs,ashwinrayaprolu1984/ringojs,ringo/ringojs,ringo/ringojs,Transcordia/ringojs,ringo/ringojs,oberhamsi/ringojs,ringo/ringojs,Transcordia/ringojs,ashwinrayaprolu1984/ringojs,ashwinrayaprolu1984/ringojs,oberhamsi/ringojs,Transcordia/ringojs,Transcordia/ringojs