ext/openssl/ossl_pkey_rsa.c
  ext/openssl/ossl_pkey_dsa.c
  ext/openssl/ossl_pkey_ec.c: Forbid export passwords that are less
  than four characters long, as OpenSSL itself does not allow this.
  Issue found by Eric Hodel.
* ext/openssl/ossl_pkey_ec.c: Add export as an alias of to_pem,
  following the PKey interface contract.
* test/openssl/test_pkey_dsa.rb
  test/openssl/test_pkey_rsa.rb
  test/openssl/test_pkey_ec.rb: Add tests that assert correct
  behaviour when dealing with passwords that are less than four
  characters long.
  [ruby-core: 42281][ruby-trunk - Bug #5951]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36001 b2dd03c8-39d4-4d8f-98ff-823fe69b080e