Auto merge of #2335 - str4d:2333-validation-speed, r=str4d

Switch to libsecp256k1-based validation for ECDSA

Cherry-picked from the following upstream PRs:

- bitcoin/bitcoin#6983
- bitcoin/bitcoin#6954

Part of #2333.

src/init.cpp

@@ -161,6 +161,7 @@ public:
 
 static CCoinsViewDB *pcoinsdbview = NULL;
 static CCoinsViewErrorCatcher *pcoinscatcher = NULL;
+static boost::scoped_ptr<ECCVerifyHandle> globalVerifyHandle;
 
 void Interrupt(boost::thread_group& threadGroup)
 {
@@ -266,6 +267,7 @@ void Shutdown()
 #endif
     delete pzcashParams;
     pzcashParams = NULL;
+    globalVerifyHandle.reset();
     ECC_Stop();
     LogPrintf("%s: done\n", __func__);
 }
@@ -661,8 +663,7 @@ void ThreadImport(std::vector<boost::filesystem::path> vImportFiles)
 bool InitSanityCheck(void)
 {
     if(!ECC_InitSanityCheck()) {
-        InitError("OpenSSL appears to lack support for elliptic curve cryptography. For more "
-                  "information, visit https://en.bitcoin.it/wiki/OpenSSL_and_EC_Libraries");
+        InitError("Elliptic curve cryptography sanity check failure. Aborting.");
         return false;
     }
     if (!glibc_sanity_test() || !glibcxx_sanity_test())
@@ -1044,6 +1045,7 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
 
     // Initialize elliptic curve code
     ECC_Start();
+    globalVerifyHandle.reset(new ECCVerifyHandle());
 
     // Sanity check
     if (!InitSanityCheck())