Properly handle license for aho-corasick code.

From Steve Watt

"""
1) It looks like this was not developed as part of Flume but brought
in from outside. Shouldn't this be in the lib directory as a
dependency binary JAR instead of source in the SRC dir?

2) The ahocorasick source files refer to a contributor license
agreement that describes the terms of use for this package inside the
NOTICES file. I can't find a notices file that came down with
flume-0.9.1.tar.gz that I got from the flume github repository. I can
find the NOTICES file on the source on GitHub for 0.9.1 but it does
not mention ahocorasick. I did find this on the web -
http://git.hashcollision.org/projects/ahocorasick_java/LICENSE - Is
this the right license for it?
"""