lei: test SIGPIPE, stop xsearch workers on client abort
The new test ensures consistency between oneshot and
client/daemon users. Cancelling an in-progress result now also
stops xsearch workers to avoid wasted CPU and I/O.
Note the lei->atfork_child_wq usage changes, it is to workaround
a bug in Perl 5: http://nntp.perl.org/group/perl.perl5.porters/258784
<CAHhgV8hPbcmkzWizp6Vijw921M5BOXixj4+zTh3nRS9vRBYk8w@mail.gmail.com>
This switches the internal protocol to use SOCK_SEQPACKET
AF_UNIX sockets to prevent merging messages from the daemon to
client to run pager and kill/exit the client script.