www/libwww: Update to 5.4.2, Fix security vulnerabilities
This a security release for libwww to take into account security advisories
CVE-2016-9063 and CVE-2017-9233.
In order to take into account current and future expat security advisories,
the expat source code was removed from the libwww tree. The makefiles were
modified so that libwww dynamically links against the system's expat library.
Patches removed were incorporated upstream.
Bump PORTREVISION of dependent ports due shlib change.
Changes: https://raw.githubusercontent.com/w3c/libwww/5.4.2/ChangeLog
MFH: 2018Q3
Security: e375ff3f-7fec-11e8-8088-28d244aee256