Fix compiler warnings

Author: teusbenschop

filter/string.cpp

@@ -2274,7 +2274,7 @@ void hex_dump (const void* addr, const int len)
 
   int i;
   unsigned char buff[per_line+1];
-  const unsigned char* pc = (const unsigned char*)addr;
+  const unsigned char* pc = static_cast<const unsigned char*>(addr);
 
   // Process every byte in the data.
   for (i = 0; i < len; i++) {

unittests/http.cpp

@@ -61,7 +61,7 @@ TEST (http, parse_post)
   using container = std::vector<std::pair<std::string,std::string>>;
 
   // Test POST data of type application/x-www-form-urlencoded.
-  for (const std::string content_type : {
+  for (const std::string& content_type : {
     std::string(application_x_www_form_urlencoded),
     std::string(application_x_www_form_urlencoded) + "; charset=UTF-8",
   }) {