* ext/socket/unixsocket.c (rsock_init_unixsock): use rb_inspect()
  because rb_sys_fail_str() fails if its argument contains NUL.

* test/socket/test_unix.rb: related test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38991 b2dd03c8-39d4-4d8f-98ff-823fe69b080e