Ignore SIGPIPE on all platforms emitting it.

* Boost ASIO should do it but unfortunately it seems it does not on OS X and Linux.
  See http://www.boost.org/doc/libs/1_55_0/boost/asio/io_service.hpp
  and http://stackoverflow.com/a/12387971/388803.
* This prevents being killed in the OPI when
  the process can not write to its Tk window anymore.
  (It is also unreasonable to kill the whole process in a multi-VM world)