Fix T45381: Crash Blender 2.75 in Win7 x64 AMD card

Previous fix didn't work well enough because on Windows Python has different
environment than Blender ans setting variables in there made no effect from
Blender point of view.

intern/cycles/blender/blender_python.cpp

@@ -22,6 +22,7 @@
 #include "blender_session.h"
 
 #include "util_foreach.h"
+#include "util_logging.h"
 #include "util_md5.h"
 #include "util_opengl.h"
 #include "util_path.h"
@@ -486,6 +487,15 @@ static PyObject *system_info_func(PyObject * /*self*/, PyObject * /*value*/)
 	return PyUnicode_FromString(system_info.c_str());
 }
 
+#ifdef WITH_OPENCL
+static PyObject *opencl_disable_func(PyObject * /*self*/, PyObject * /*value*/)
+{
+	VLOG(2) << "Disabling OpenCL platform.";
+	setenv("CYCLES_OPENCL_TEST", "NONE", 1);
+	Py_RETURN_NONE;
+}
+#endif
+
 static PyMethodDef methods[] = {
 	{"init", init_func, METH_VARARGS, ""},
 	{"create", create_func, METH_VARARGS, ""},
@@ -501,6 +511,9 @@ static PyMethodDef methods[] = {
 #endif
 	{"available_devices", available_devices_func, METH_NOARGS, ""},
 	{"system_info", system_info_func, METH_NOARGS, ""},
+#ifdef WITH_OPENCL
+	{"opencl_disable", opencl_disable_func, METH_NOARGS, ""},
+#endif
 	{NULL, NULL, 0, NULL},
 };