For usages of assert() that are meant to persist in Release builds (when NDEBUG is defined), replace those usages with persistent alternatives

Remove software exception translator function, simplifying exception handler
macros.  FatalSystemExceptions are left unhandled.

Two new configuration options are added:
     - "enable_ipv6" to enable/disable the overall use of IPv6
     - "ipv6_server" to enable/disable the use of IPv6 sockets when running
       a server (when "enable_ipv6" is enabled)

Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors

Use the logger; also, default to not showing much crap in console. Use --info-on-stderr to enable crap.