added alsa

Original commit message from CVS:
added alsa
diff --git a/configure.ac b/configure.ac
index 89fe6d4..1e4660c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1152,6 +1152,7 @@
 ext/Makefile
 ext/a52/Makefile
 ext/aalib/Makefile
+ext/alsa/Makefile
 ext/audiofile/Makefile
 ext/esd/Makefile
 ext/lame/Makefile