if libtiff not found disable on unix.

CMakeLists.txt

@@ -125,11 +125,9 @@ IF(UNIX AND NOT APPLE)
 
 	IF(WITH_OPENAL)
 		FIND_PACKAGE(OpenAL)
-		IF(OPENAL_FOUND)
-			SET(WITH_OPENAL ON)
-		ELSE(OPENAL_FOUND)
+		IF(NOT OPENAL_FOUND)
 			SET(WITH_OPENAL OFF)
-		ENDIF(OPENAL_FOUND)
+		ENDIF(NOT OPENAL_FOUND)
 	ENDIF(WITH_OPENAL)
 
 	IF(WITH_JACK)
@@ -217,7 +215,10 @@ IF(UNIX AND NOT APPLE)
 	SET(LIBSAMPLERATE_LIBPATH ${LIBSAMPLERATE}/lib)
 
 	IF(WITH_TIFF)
-		FIND_PACKAGE(TIFF REQUIRED)
+		FIND_PACKAGE(TIFF)
+		IF(NOT TIFF_FOUND)
+			SET(WITH_TIFF OFF)
+		ENDIF(NOT TIFF_FOUND)
 	ENDIF(WITH_TIFF)
 
 	FIND_PACKAGE(JPEG REQUIRED)