Dsound hle fix (#539)

* Turned g_bEmuException into a thread_local variable (this fixes issue #135)

* Added DirectSoundUseFullHRTF to XTL namespace

This is a requirement for functions to be patched!
(Spotted this by chance while looking at the exports of our Cxbx.exe
using CFF Explorer VIII)

src/CxbxKrnl/EmuDSound.cpp

@@ -2488,7 +2488,9 @@ HRESULT WINAPI XTL::EMUPATCH(IDirectSoundBuffer_SetFormat)
 // ******************************************************************
 // * patch: DirectSoundUseFullHRTF
 // ******************************************************************
-STDAPI_(void) EMUPATCH(DirectSoundUseFullHRTF)(void)
+STDAPI_(void) XTL::EMUPATCH(DirectSoundUseFullHRTF)
+(
+    void)
 {
     FUNC_EXPORTS;