Use the character based overload for std::string::find.

std::string::find has a character based overload as can be seen here
(4th oveload): http://www.cplusplus.com/reference/string/string/find/

Use that instead of constantly allocating temporary strings.

src/rpc/client.cpp

@@ -213,7 +213,7 @@ UniValue RPCConvertNamedValues(const std::string &strMethod, const std::vector<s
     UniValue params(UniValue::VOBJ);
 
     for (const std::string &s: strParams) {
-        size_t pos = s.find("=");
+        size_t pos = s.find('=');
         if (pos == std::string::npos) {
             throw(std::runtime_error("No '=' in named argument '"+s+"', this needs to be present for every argument (even if it is empty)"));
         }