squash-cherry-pick pr #15 by takezawa-san
report name of the temporary-created lock file on error
check error of ```IO::Handle->blocking()``` by calling ```defined``` (fixes server crash on osx when bound to multiple ports)
Merge branch 'master' into kazuho/pr/15
fix deadlock on flock(LOCK_EX) on OS X
Merge branch 'kazuho/pr/15'