Mac: Further qmake config tweaks

Allow defining SDL framework dir in config_user.pri.
Also don't use the default Qt include and library
directories when using a specific SDK package, because
that would mess with the include paths (frameworks in the
SDK will include the wrong headers).

doomsday/config.pri

@@ -147,12 +147,12 @@ macx {
         QMAKE_MAC_SDK = /Developer/SDKs/MacOSX10.4u.sdk
         QMAKE_CFLAGS += -mmacosx-version-min=10.4
         DEFINES += MACOS_10_4
-        CONFIG += x86 ppc
-
-        # Not using Qt, and anyway these would not point to the 10.4u SDK.
-        QMAKE_INCDIR_QT = ""
-        QMAKE_LIBDIR_QT = ""
+        CONFIG += x86 ppc       
     }
+
+    # Not using Qt, and anyway these would not point to the chosen SDK.
+    QMAKE_INCDIR_QT = ""
+    QMAKE_LIBDIR_QT = ""
 
     defineTest(useFramework) {
         LIBS += -framework $$1

doomsday/dep_libpng.pri

@@ -16,7 +16,7 @@ else:macx {
     } else {
         # Use a static libpng from MacPorts (ppc+i386).
         INCLUDEPATH += /opt/local/include
-		LIBS += /opt/local/lib/libpng.a
+        LIBS += /opt/local/lib/libpng.a
     }
 }
 else {

doomsday/dep_sdl.pri

@@ -28,7 +28,9 @@ win32 {
 }
 else:macx {
     # Mac OS X.
-    SDL_FRAMEWORK_DIR = $$(HOME)/Library/Frameworks
+    isEmpty(SDL_FRAMEWORK_DIR) {
+        error("dep_sdl: SDL framework path not defined, check your config_user.pri")
+    }
 
     INCLUDEPATH += \
         $${SDL_FRAMEWORK_DIR}/SDL.framework/Headers \