BUG/MEDIUM: unix: do not unlink() abstract namespace sockets upon failure.

When bind() fails (function uxst_bind_listener()), the fail path doesn't
consider the abstract namespace and tries to unlink paths held in
uninitiliazed memory (tempname and backname). See the strace excerpt;
the strings still hold the path from test1.

===============================================================================================
23722 bind(5, {sa_family=AF_FILE, path=@"test2"}, 110) = -1 EADDRINUSE (Address already in use)
23722 unlink("/tmp/test1.sock.23722.tmp") = -1 ENOENT (No such file or directory)
23722 close(5)                          = 0
23722 unlink("/tmp/test1.sock.23722.bak") = -1 ENOENT (No such file or directory)
===============================================================================================

This patch should be backported to 1.5.
DOC: provide an example of how to use ssl_c_sha1

As suggested by Aydan Yumerefendi, a little bit of examples never hurts.