* ext/openssl/ossl_ssl.c: Add SSL constants and allow to unset SSL
  option to prevent BEAST attack. See [Bug #5353].

  In OpenSSL, OP_DONT_INSERT_EMPTY_FRAGMENTS is used to prevent
  TLS-CBC-IV vulunerability described at
  http://www.openssl.org/~bodo/tls-cbc.txt
  It's known issue of TLSv1/SSLv3 but it attracts lots of attention
  these days as BEAST attack. (CVE-2011-3389)

  Until now ossl sets OP_ALL at SSLContext allocation and call
  SSL_CTX_set_options at connection.  SSL_CTX_set_options updates the
  value by using |= so bits set by OP_ALL cannot be unset afterwards.
  This commit changes to call SSL_CTX_set_options only 1 time for each
  SSLContext. It sets the specified value if SSLContext#options= are
  called and sets OP_ALL if not.

  To help users to unset bits in OP_ALL, this commit also adds several
  constant to SSL such as
  OpenSSL::SSL::OP_DONT_INSERT_EMPTY_FRAGMENTS.  These constants were
  not exposed in Ruby because there's no way to unset bits in OP_ALL
  before.

  Following is an example to enable 0/n split for BEAST prevention.

    ctx.options = OP_ALL & ~OP_DONT_INSERT_EMPTY_FRAGMENTS

* test/openssl/test_ssl.rb: Test above option exists.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_9_3@34524 b2dd03c8-39d4-4d8f-98ff-823fe69b080e