Use OpenAL_SOURCE_DIR for the CMake module path and declare the project earlier

The minimum CMake version required is also bumped to 2.6. Patch by Andrew West,
allows OpenAL Soft to be properly built as a sub-project.

CMakeLists.txt

@@ -1,13 +1,15 @@
 # CMake build file list for OpenAL
 
-CMAKE_MINIMUM_REQUIRED(VERSION 2.4)
+CMAKE_MINIMUM_REQUIRED(VERSION 2.6)
+
+PROJECT(OpenAL)
 
 IF(COMMAND CMAKE_POLICY)
   CMAKE_POLICY(SET CMP0003 NEW)
   CMAKE_POLICY(SET CMP0005 NEW)
 ENDIF(COMMAND CMAKE_POLICY)
 
-SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
+SET(CMAKE_MODULE_PATH "${OpenAL_SOURCE_DIR}/cmake")
 
 INCLUDE(CheckFunctionExists)
 INCLUDE(CheckLibraryExists)
@@ -20,9 +22,6 @@ INCLUDE(CheckCSourceCompiles)
 INCLUDE(CheckTypeSize)
 
 
-PROJECT(OpenAL)
-
-
 SET(CMAKE_ALLOW_LOOSE_LOOP_CONSTRUCTS TRUE)