gsdx-ogl: improve debug of stencil

Note: ENABLE_OGL_STENCIL_DEBUG could be dropped now that I can read the stencil properly

plugins/GSdx/GSDeviceOGL.cpp

@@ -962,6 +962,7 @@ void GSDeviceOGL::SetupDATE(GSTexture* rt, GSTexture* ds, const GSVertexPT1* ver
 #ifdef ENABLE_OGL_STENCIL_DEBUG
 	const GSVector2i& size = rt->GetSize();
 	GSTexture* t = CreateRenderTarget(size.x, size.y, false);
+	ClearRenderTarget(t, 0);
 #else
 	GSTexture* t = NULL;
 #endif

plugins/GSdx/GSDeviceOGL.h

@@ -180,7 +180,7 @@ public:
 	{
 		// Only needed once since m_stencil_mask is constant
 		// Control which stencil bitplane are written
-		glStencilMask(1);
+		glStencilMask(0xFF);
 	}
 
 	void EnableDepth() { m_depth_enable = true; }

plugins/GSdx/GSTextureFXOGL.cpp

@@ -51,6 +51,10 @@ void GSDeviceOGL::CreateTextureFX()
 			m_vs[key] = CompileVS(sel, logz);
 	}
 
+	// Enable all bits for stencil operations. Technically 1 bit is
+	// enough but buffer is polluted with noise. Clear will be limited
+	// to the mask.
+	glStencilMask(0xFF);
 	for (uint32 key = 0; key < OMDepthStencilSelector::size(); key++)
 		m_om_dss[key] = CreateDepthStencil(OMDepthStencilSelector(key));