fix -Wconst warnings

[ew: cleaned up the dirty union hack a bit]
Signed-off-by: Eric Wong <normalperson@yhbt.net>

git-svn-id: https://svn.musicpd.org/mpd/trunk@7180 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/inputStream_http.c

@@ -187,7 +187,8 @@ static char *base64Dup(char *s)
 	return ret;
 }
 
-static char *authString(char *header, char *user, char *password)
+static char *authString(const char *header,
+			const char *user, const char *password)
 {
 	char *ret = NULL;
 	int templen;