Better handle the INCLUDE_DIRECTORIES property

Older cmake verions (prior to 2.8.8) don't have a per-target
INCLUDE_DIRECTORIES property, so the directories have to be
added using the INCLUDE_DIRECTORIES command.

CMakeLists.txt

@@ -131,7 +131,10 @@ ENDIF()
 
 
 # Add definitions, compiler switches, etc.
-INCLUDE_DIRECTORIES("include" "${OpenAL_BINARY_DIR}")
+INCLUDE_DIRECTORIES("${OpenAL_SOURCE_DIR}/include" "${OpenAL_BINARY_DIR}")
+IF(CMAKE_VERSION VERSION_LESS "2.8.8")
+    INCLUDE_DIRECTORIES("${OpenAL_SOURCE_DIR}/OpenAL32/Include")
+ENDIF()
 
 IF(NOT CMAKE_BUILD_TYPE)
     SET(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING
@@ -773,6 +776,9 @@ IF(ALSOFT_EXAMPLES)
     FIND_PACKAGE(SDL)
     IF(SDL_FOUND)
         FIND_PACKAGE(SDL_sound)
+        IF(CMAKE_VERSION VERSION_LESS "2.8.8")
+            INCLUDE_DIRECTORIES(${SDL_INCLUDE_DIR} ${SDL_SOUND_INCLUDE_DIR})
+        ENDIF()
     ENDIF()
 ENDIF()