net-p2p/amule: fix build with Boost-1.89 (+)

Backport recent boost.m4 (inspired by upstream PR https://github.com/amule-project/amule/pull/361)
autoconf2.70 support to deal with updated boost.m4
Add missed #include <boost/asio/deadline_timer.hpp>
Add missed #include <exception>
Disable online version check
Switch to xdg-open instead of direct call of mplayer

Reported by: fallout, eduardo
Approved by: eduardo