FileAnalysis: add custom libmagic database.

- It's derived from the magic database of libmagic 5.14, but with most
  everything not related to mime types removed.

- The custom database is always used by default for mime detection, but
  the more verbose file type detection will fall back on the default
  libmagic installation's database.  The result is: mime type strings
  are now guaranteed to be consistent across platforms, but the verbose
  file type descriptions are not.

- The custom database gets installed in $prefix/share/bro/magic, and
  should even be extensible if files with new patterns are added inside
  the directory.

- The search path for the mime magic database can be controlled via
  BROMAGIC environment variable.

- Remove mime_desc field from ftp.log.

- Stop using the mime/file type canonifier with unit tests.

- libmagic >= 5.04 is now a requirement.

magic/javascript

@@ -0,0 +1,17 @@
+# See COPYING file in this directory for original libmagic copyright.
+#------------------------------------------------------------------------------
+# $File: $
+# javascript:  magic for javascript and node.js scripts.
+#
+0	search/1/w	#!/bin/node		Node.js script text executable
+!:mime application/javascript
+0	search/1/w	#!/usr/bin/node		Node.js script text executable
+!:mime application/javascript
+0	search/1/w	#!/bin/nodejs		Node.js script text executable
+!:mime application/javascript
+0	search/1/w	#!/usr/bin/nodejs	Node.js script text executable
+!:mime application/javascript
+0	search/1	#!/usr/bin/env\ node	Node.js script text executable
+!:mime application/javascript
+0	search/1	#!/usr/bin/env\ nodejs	Node.js script text executable
+!:mime application/javascript