Don't block all signals.
Some (buggy?) thread implementations use RT signals internally... The handling of SIGPIPE remains somewhat problematic. We should probably use MSG_NOSIGNAL when writing to sockets, but this does not work when dealing with pipes/FIFOs or writing to sockets using write(). In particular, net_Write uses write() so that it can be used on non-socket descriptors too (I believe this is used by the RC interface).