Add support for localAddress

When we make outgoing requests, we may want to bind to a specific local
address. This change allows the localAddress property to be specified
via the options object.
Merge branch 'customizeOutgoingAddress' of github.com:sberan/node-http-proxy into sberan-customizeOutgoingAddress

Conflicts:
	lib/http-proxy.js
	lib/http-proxy/common.js