qmake|Win32: Fixed tests.pro, added "deng_nodirectsound" option

The main config.pri was not being included from tests.pro, which meant
that the user's configuration was not being applied.

CONFIG+=deng_nodirectsound will disable the DirectSound sound driver.

doomsday/config.pri

@@ -16,6 +16,7 @@
 # - deng_fluidsynth             Build the FluidSynth sound driver
 # - deng_fmod                   Build the FMOD Ex sound driver
 # - deng_nativesdk              (Mac) Use current OS's SDK for non-distrib use
+# - deng_nodirectsound          (Windows) Disable the DirectSound sound driver
 # - deng_nodisplaymode          Disable native display mode changes
 # - deng_nofixedasm             Disable assembler fixed-point math
 # - deng_noopenal               Disable building of the OpenAL sound driver

doomsday/plugins/plugins.pro

@@ -20,4 +20,7 @@ deng_fmod: SUBDIRS += fmod
 deng_fluidsynth: SUBDIRS += fluidsynth
 
 # Platform-specific plugins.
-win32: SUBDIRS += directsound winmm
+win32 {
+    !deng_nodirectsound: SUBDIRS += directsound
+    SUBDIRS += winmm
+}

doomsday/tests/tests.pro

@@ -1,3 +1,8 @@
+# The Doomsday Engine Project
+# Copyright (c) 2012 Jaakko Keränen <jaakko.keranen@iki.fi>
+
+include(../config.pri)
+
 TEMPLATE = subdirs
 
 deng_tests: SUBDIRS += \