Change alut includes to <AL/alut.h>

Alut's pkg-config definition only adds the top-level include directory
containing the AL directory to the include paths. This works on most
platforms because OpenAL adds that AL directory. However, with nix,
these two directories are distinct and the build fails.

src/platform/C4MusicFile.cpp

@@ -30,7 +30,7 @@
 // This is an ugly hack to make FreeALUT not dllimport everything.
 #define _XBOX
 #endif
-#include <alut.h>
+#include <AL/alut.h>
 #undef _XBOX
 #endif
 #define alErrorCheck(X) do { X; { ALenum err = alGetError(); if (err) LogF("al error: %s (%x)", #X, err); } } while (0)

src/platform/C4SoundIncludes.h

@@ -35,7 +35,7 @@
  		// This is an ugly hack to make FreeALUT not dllimport everything.
 #		define _XBOX
 #	endif
-#	include <alut.h>
+#	include <AL/alut.h>
 #	undef _XBOX
 #	if defined(__APPLE__)
 #		import <CoreFoundation/CoreFoundation.h>