build: only use DESTDIR instead of PREFIX for pkg

Preserve default install prefix seen in process.config, but use DESTDIR
for installing to deliniate 32/64 versions, avoid conflicts with PREFIX
settings in config.mk
test: reap children when cluster-bind-twice fails
test: report test duration in TAP progress
stream_wrap: remove unused arg from WriteBuffer

WriteBuffer was changed in the cork/uncork implementation (60ed2c54).
The unused argument has been removed.
stream_wrap: fix memory leak on early return
test: don't use total_seconds() because of py2.6
Merge remote-tracking branch 'upstream/master'