add aac file type to file(1); from steve simon.

Reference: /n/atom/patch/applied2013/fileaac
Date: Fri Sep 20 14:48:14 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/file.c	Fri Sep 20 14:47:56 2013
+++ /sys/src/cmd/file.c	Fri Sep 20 14:47:57 2013
@@ -540,6 +540,7 @@
 	070707,		0xFFFF,		"cpio archive\n", OCTET,
 	0x2F7,		0xFFFF,		"tex dvi\n", "application/dvi",
 	0xfaff,		0xfeff,		"mp3 audio\n",	"audio/mpeg",
+	0xf0ff,		0xf6ff,		"aac audio\n",	"audio/mpeg",
 	0xfeff0000,	0xffffffff,	"utf-32be\n",	"text/plain charset=utf-32be",
 	0xfffe,		0xffffffff,	"utf-32le\n",	"text/plain charset=utf-32le",
 	0xfeff,		0xffff,		"utf-16be\n",	"text/plain charset=utf-16be",