Improve Stream Component test coverage

Hi,

I've improved the test coverage of Camel Stream component.

In particular I've added:

a) tests for Stream producer writing to the URL output stream (StreamToUrlTest).

b) assertions to StreamSystemOutTest. Previously we've been sending a messages to the System.out but made no assertions about it. This looked like the AssertionFreeTesting [1]. I changed the test to temporarily switch System.out with another PrintStream instance so we could make some assertions on it.

Could somebody take a look at patch and possibly apply it to the trunk?

[1] http://martinfowler.com/bliki/AssertionFreeTesting.html