Stop sending SIGPIPE to debuggerd.

SIGPIPE is a pretty normal way for command-line apps to die, but because
we catch it and report it via debuggerd, we get a lot of bogus bugs. We
could catch SIGPIPE in our tools, but that's not really legit and slightly
misleading.

"But", you say, "catching SIGPIPE is useful for app bugs!". Except a trawl
through buganizer suggests it's misleading there too. Not least because
it's usually an innocent victim that dies --- the problem is usually on the
other end of the pipe (which you learn nothing about because that process
already died, which is what closed the pipe).

We also don't catch SIGALRM, which is another signal that will terminate
your process if you don't catch it, but that one actually represents a
logic error in the crashing process, so there's a stronger argument for
catching that. (Except it too is not a real source of bugs.)

Bug: http://b/20659371
Change-Id: I79820b36573ddaa9a7bad0561a52f23e7a8d15ac