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- created a uniform shim layer for the Go code to invoke that does the
  right thing depending on the version of openssl. functions that have
  yet to be moved can be done so as needed.

- fixed the incorrect use of X509_STORE_CTX_get_app_data in verify_cb to
  pull out the SSL object from the x509 store context, which causes
  crashes when the SSL object index happens to not be zero.

- fix engine not being passed to HMAC_Init_ex

- fix HMAC tests not checking for failures with NewHMAC

As pointed out by ishbir in issue 24, the applyKeyAndIV function was
incorrectly always using EVP_EncryptInit_ex(), even when the underlying
context being initialized was for a decryption.

This change causes it to select the right initializer based on the
"encrypt" field in the EVP_CIPHER_CTX. A test is also added which
verifies a fix.

Closes #24.

NID is also now an exposed type

Change-Id: I4642fb9b97256ec6b3ffbe403272efc690bf1606

since it doesn't have gcm stuff put it in a conditionally built
file.

Change-Id: I8083ff9b86b6fe0723fd21ffc77038b7679c97c7

[katamari commit: 40d84e93b0bf20707c02cdbdaec154a0d387043d]

[katamari commit: 0a645f84cf1bd058f7533e8eaceba32c75fae90e]