Fix some autotools related problems

Huge thanks to gnarlie for helping me find and diagnose
several problems stemming from autogen.sh on FreeBSD 6.1

We require autoconf 2.58 for autogen.sh, but it seems like
that's always been the case, we just never caught it before :/

"bash ./configure" just about sums up what I want to do right now...

git-svn-id: https://svn.musicpd.org/mpd/trunk@4384 09075e82-0dd4-0310-85a5-a0d7c8717e4f

configure.ac

@@ -1,7 +1,7 @@
 dnl AC_INIT(src/main.c)
 dnl AM_INIT_AUTOMAKE(mpd, 0.12.0)
 
-AC_PREREQ(2.52)
+AC_PREREQ(2.58)
 AC_INIT(mpd, 0.12.0, warren.dukes@gmail.com)
 AM_INIT_AUTOMAKE($PACKAGE_NAME, $PACKAGE_VERSION)
 
@@ -234,7 +234,11 @@ if test x$enable_id3 = xyes; then
 	CFLAGS=$oldcflags
 	LIBS=$oldlibs
 	CPPFLAGS=$oldcppflags
-	AC_DEFINE(HAVE_ID3TAG,1,[Define to use id3tag])
+	if $use_libid3tag = xyes; then
+		AC_DEFINE(HAVE_ID3TAG,1,[Define to use id3tag])
+	else
+		enable_id3=no
+	fi
 fi
 
 MAD_SUBDIR=""
@@ -274,7 +278,11 @@ if test x$enable_mp3 = xyes; then
 	CFLAGS=$oldcflags
 	LIBS=$oldlibs
 	CPPFLAGS=$oldcppflags
-	AC_DEFINE(HAVE_MAD,1,[Define to use libmad])
+	if test x$use_libmad = xyes; then
+		AC_DEFINE(HAVE_MAD,1,[Define to use libmad])
+	else
+		enable_mp3=no
+	fi
 fi
 
 if test x$enable_mpc = xyes; then