Cross-compiling MinGW issue - case sensitivity

[norru]

I am cross-compiling openfx-opencv plugins for Windows from Linux and I've found two minor case sensitivity issues when building openfx as a dependency.

1. In Support/include/ofxsHWNDInteract.h

#include <Windows.h> should be

#include <windows.h>

as the MinGW header is all lowercase.

2. in Support/Library/ofxsSupportPrivate.h

#include "ofxsHWndInteract.h" should be

#include "ofxsHWNDInteract.h"

The fixes are trivial if done manually but cause problems when automating the build/reproducing the build (as they require either a source tweak or a toolchain tweak).