Duplicated the expression that writes to std out

upon test completion, in the NUnit Glue Library. While this introduces
seemingly redundant duplication, this prepares the code for the next
change, which is to make the output upon success configurable.

Since there are no automated tests covering the NUnit Glue Libraries, I
find it most prudent to proceed in baby steps.
Moved binding of attr up,

because soon, the attr value is going to be required from the the
testRunner object, where the OnFinished method will need to close over one
of the properties of the [<Property>] attribute.
Added a QuietOnSuccess property to NUnit Property

attribute.

Although no automated tests cover this, I also added an example of using
this property to the example library, and executed this small test suite
with the NUnit GUI runner, as well as the NUnit command-line runner, and
manually verified that no output was produced by the new noOutputOnSuccess
example Property.
Merge pull request #66 from ploeh/make-it-possible-to-tell-nunit-to-be-quiet-on-success

Make it possible to tell nunit to be quiet on success