feature: SSL/TLS cosocket API

* added new method sslhandshake() to the stream-typed cosocket objects.
* added new configuration directives lua_ssl_trusted_certificate,
  lua_ssl_verify_depth, lua_ssl_crl, lua_ssl_protocols, and
  lua_ssl_ciphers.

Thanks aviramc for the original patch in #290.
tests: fixed the test case added in commit 6ef948150.
tests: one minor Perl code style fix.
bugfix: memory leak cound happen when both cosocket connection pools and "lua_code_cache off" were used. this regression had appeared in the ssl cosocket patch, i.e., commit 5aed1966.