Reload is an async operation on WP8 (if it'd be a blocking one, we would end up with a deadlock due to the threading on the platform). The caller doesn't know when we finished working with the stream, therefore we need to dispose the texture stream inside MonoGame.
Merge branch 'wp8_texture2d_reload_disposefix' of https://github.com/SongArc/MonoGame into pr2959

Conflicts:
	MonoGame.Framework/Graphics/Texture2D.DirectX.cs