Bug 896 - Avoid race conditions reading message from exited process

Bug 896 - Avoid race conditions reading message from exited process

Patch based on extensive work from Michael Meeks <michael.meeks@novell.com>,
thanks to Dafydd Harries <dafydd.harries@collabora.co.uk>,
Kimmo Hämäläinen <kimmo.hamalainen@nokia.com> and others.

The basic idea with this bug is that we effectively ignore errors
on write.  Only when we're done reading from a connection do we
close down a connection.  This avoids a race condition where
if a process (such as dbus-send) exited while we still had
data to read in the buffer, we'd miss that data.