* SoundPlayer.cs: Addded support for playing WAV files on Windows.

* SoundPlayer.cs: Addded support for playing WAV files on Windows.
Fixed ctor (Stream) to allow null argument. In LoadFromUri, first
reset mstream to support resetting Stream to null. Support playing
default sound. Allow Stream to be set to null. Reset AudioData and
WaveData when new stream is loaded.
* Win32SoundPlayer.cs: Wrapper for PlaySound Win32 API.
* System.dll.sources: Added Win32SoundPlayer.cs.
* SoundPlayerTest.cs: Added trivial ctor tests. Added test for
Stream property.

svn path=/trunk/mcs/; revision=89112