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/java

@@ -0,0 +1,16 @@
+# See COPYING file in this directory for original libmagic copyright.
+#------------------------------------------------------------
+# $File: java,v 1.13 2011/12/08 12:12:46 rrt Exp $
+# Java ByteCode and Mach-O binaries (e.g., Mac OS X) use the
+# same magic number, 0xcafebabe, so they are both handled
+# in the entry called "cafebabe".
+#------------------------------------------------------------
+
+0	belong		0xfeedfeed	Java KeyStore
+!:mime	application/x-java-keystore
+0	belong		0xcececece	Java JCE KeyStore
+!:mime	application/x-java-jce-keystore
+
+# Java source
+0	regex	^import.*;$	Java source
+!:mime	text/x-java