* lib/securerandom.rb (gen_random): to avoid blocking on Windows.
	  On Windows OpenSSL RAND_bytes (underlying implementation is
	  RAND_poll in crypto/rand/rand_win.c) may be blocked at
	  NetStatisticsGet.
	  https://wiki.openssl.org/index.php/Random_Numbers#Windows_Issues
	  Instead of this, use Random.raw_seed directory (whose implementation
	  CryptGenRandom is one of the source of
	  entropy of RAND_poll on Windows).
	  https://wiki.openssl.org/index.php/Random_Numbers
	  Note: CryptGenRandom function is PRNG and doesn't check its entropy,
	  so it won't block. [Bug #12139]
	  https://msdn.microsoft.com/ja-jp/library/windows/desktop/aa379942.aspx
	  https://tools.ietf.org/html/rfc4086#section-7.1.3
	  https://eprint.iacr.org/2007/419.pdf
	  http://www.cs.huji.ac.il/~dolev/pubs/thesis/msc-thesis-leo.pdf
	  Instead of this, use Random.raw_seed directly (whose implementation


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