Fix handling of SIGPIPE

Do not ignore SIGPIPE beause that is inherited by child processes and it screws up shell scripts. Instead, install a handler that does nothing.

The package "pa_ovisitor" fails on my machine: it just loops, eating one core, because its build instructions include "yes no | omake <something>". When omake is done, the "yes" process ignores the SIGPIPE and just loops forever.