* lib/securerandom.rb (SecureRandom.random_bytes): modify PRNG state
  to prevent random number sequence repeatation at forked
  child process which has same pid.
  reported by Eric Wong.  [ruby-core:35765]

backport r32124 by nahi

* test/test_securerandom.rb: Add testcase.  This testcase does NOT aim
  to test cryptographically strongness and randomness.  It includes
  the test for PID recycle issue of OpenSSL described in #4579 but
  it's disabled by default.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8_7@32128 b2dd03c8-39d4-4d8f-98ff-823fe69b080e