SignalHandler::entry spins the cpu and never sleeps

SignalHandler::entry shouldn't poll for POLLOUT.  It never
actually writes to the pipes in question.  Polling for POLLOUT
causes poll(2) to immediately return, so the function spins the
CPU and never blocks.  Tested on FreeBSD 9.1 amd64

Signed-off-by: Alan Somers <asomers@gmail.com>
configure.ac: fix typo setting UUID_LIBS

Signed-off-by: Alan Somers <asomers@gmail.com>
ipaddr: define s6_addr16 on FreeBSD

An older version of wip-port included this fix, but it got dropped as
of 2013-09-30

Signed-off-by: Alan Somers <asomers@gmail.com>
FileJournal: use O_SYNC if O_DSYNC is undefined

O_DSYNC is not defined on all platforms.  O_SYNC offers stronger
consistency guarantees at the expense of possibly reduced performance.
In fact, open(2) tells me that as of 2.6.31, the two flags are
synonymous on Linux.  This patch fixes the build on FreeBSD

Signed-off-by: Alan Somers <asomers@gmail.com>
build: Restrict OSX-specific linker flags to OSX

"-undefined" and "-flat-namespace" are only recognized on the OSX
version of gcc.  On FreeBSD, they are ignored, and the argument to
"-undefined" is treated as a missing file argument.  This patch is based
off of the 2013-9-30 version of wip-port.

Signed-off-by: Alan Somers <asomers@gmail.com>
compat: add compat.h

During one of your rebases from master to wip-port, the inclusion of
include/compat.h got dropped from a bunch of files.  As of 2013-09-30,
these patches are needed on FreeBSD

Signed-off-by: Alan Somers <asomers@gmail.com>