ext/socket/unixsocket.c (rsock_init_unixsock): check the result of listen(2). based on a patch from Mike Pomraning. [ruby-core:23698] git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@27272 b2dd03c8-39d4-4d8f-98ff-823fe69b080e