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/python

@@ -0,0 +1,46 @@
+# See COPYING file in this directory for original libmagic copyright.
+#------------------------------------------------------------------------------
+# $File: python,v 1.21 2012/06/21 01:12:51 christos Exp $
+# python:  file(1) magic for python
+#
+
+0	search/1/w	#!\ /usr/bin/python	Python script text executable
+!:mime text/x-python
+0	search/1/w	#!\ /usr/local/bin/python	Python script text executable
+!:mime text/x-python
+0	search/1	#!/usr/bin/env\ python	Python script text executable
+!:mime text/x-python
+0	search/1	#!\ /usr/bin/env\ python	Python script text executable
+!:mime text/x-python
+
+# from module.submodule import func1, func2
+0	regex	\^from\\s+(\\w|\\.)+\\s+import.*$	Python script text executable
+!:mime text/x-python
+
+# def __init__ (self, ...):
+0	search/4096	def\ __init__
+>&0	search/64 self	Python script text executable
+!:mime text/x-python
+
+# comments
+0	search/4096	'''
+>&0	regex	.*'''$	Python script text executable
+!:mime text/x-python
+
+0	search/4096	"""
+>&0	regex	.*"""$	Python script text executable
+!:mime text/x-python
+
+# try:
+# except: or finally:
+# block
+0	search/4096	try:
+>&0	regex	\^\\s*except.*:	Python script text executable
+!:mime text/x-python
+>&0	search/4096	finally:	Python script text executable
+!:mime text/x-python
+
+# def name(args, args):
+0	regex	 \^(\ |\\t)*def\ +[a-zA-Z]+
+>&0	regex	\ *\\(([a-zA-Z]|,|\ )*\\):$ Python script text executable
+!:mime text/x-python