added hash64 function that uses sha256 to replace city_hash in blockchain and message protocol-related hashing

include/fc/crypto/sha256.hpp

@@ -81,6 +81,8 @@ class sha256
   void to_variant( const sha256& bi, variant& v );
   void from_variant( const variant& v, sha256& bi );
 
+  uint64_t hash64(const char* buf, size_t len);    
+
 } // fc
 namespace std
 {

src/crypto/elliptic.cpp

@@ -264,7 +264,7 @@ namespace fc { namespace ecc {
     std::string public_key::to_base58() const
       {
       public_key_data key = serialize();
-      uint32_t check = uint32_t(city_hash64(key.data, sizeof(key)));
+      uint32_t check = uint32_t(fc::hash64(key.data, sizeof(key)));
       assert(key.size() + sizeof(check) == 37);
       array<char, 37> data;
       memcpy(data.data, key.begin(), key.size());

src/crypto/sha256.cpp

@@ -103,4 +103,11 @@ namespace fc {
     else
         memset( &bi, char(0), sizeof(bi) );
   }
-}
+
+  uint64_t hash64(const char* buf, size_t len)
+  {
+    sha256 sha_value = sha256::hash(buf,len);
+    return sha_value._hash[0];
+  }
+
+} //end namespace fc