[master] Update 3rd party licnese issues

Instead of duplicating more third-party licenses here in LICENSE
    file (there are many), just generically suggest to see the other files.

    Per the md5 copyright license agreement, add mention of
    required verbatim advertising statement in the release notes and
    readme.

    In the RELNOTES, I also mention ISC is open source software.

    In the README, I added a HISTORY section and placed that
    advertising statement there. If the HISTORY section is not wanted,
    then remove it and just mention the required verbatim advertising statement.
    By the way, some good history is in old READMEs and at
    http://hack.org/mc/texts/dhcp-freenix.txt
    (but I can't find the official hosted Lemon version of that paper).

    Remove the advertising clause from the historical BSD
    code copyrighted by The Regents of the University of California.

    For details see
    ftp://ftp.cs.berkeley.edu/pub/4bsd/README.Impt.License.Change

    (To summarize: in 1999, the University said that distributors
    are no longer required to acknowledge within advertising and the
    paragraph in the license may be deleted.)

RELNOTES

@@ -48,6 +48,10 @@ The system has only been tested on Linux, FreeBSD, and Solaris, and may not
 work on other platforms. Please report any problems and suggested fixes to
 <dhcp-users@isc.org>.
 
+ISC DHCP is open source software maintained by Internet Systems
+Consortium.  This product includes cryptographic software written
+by Eric Young (eay@cryptsoft.com).
+
 			Changes since 4.2.0 (new features)
 
 - If a client renews before 'dhcp-cache-threshold' percent of its lease