util: name replace_file arguments better

It was confusing unless you read code and the rename(2) man page.

src/common/util.cpp

@@ -640,16 +640,16 @@ std::string get_nix_version_display_string()
     return res;
   }
 
-  std::error_code replace_file(const std::string& replacement_name, const std::string& replaced_name)
+  std::error_code replace_file(const std::string& old_name, const std::string& new_name)
   {
     int code;
 #if defined(WIN32)
     // Maximizing chances for success
     std::wstring wide_replacement_name;
-    try { wide_replacement_name = string_tools::utf8_to_utf16(replacement_name); }
+    try { wide_replacement_name = string_tools::utf8_to_utf16(old_name); }
     catch (...) { return std::error_code(GetLastError(), std::system_category()); }
     std::wstring wide_replaced_name;
-    try { wide_replaced_name = string_tools::utf8_to_utf16(replaced_name); }
+    try { wide_replaced_name = string_tools::utf8_to_utf16(new_name); }
     catch (...) { return std::error_code(GetLastError(), std::system_category()); }
 
     DWORD attributes = ::GetFileAttributesW(wide_replaced_name.c_str());
@@ -661,7 +661,7 @@ std::string get_nix_version_display_string()
     bool ok = 0 != ::MoveFileExW(wide_replacement_name.c_str(), wide_replaced_name.c_str(), MOVEFILE_REPLACE_EXISTING);
     code = ok ? 0 : static_cast<int>(::GetLastError());
 #else
-    bool ok = 0 == std::rename(replacement_name.c_str(), replaced_name.c_str());
+    bool ok = 0 == std::rename(old_name.c_str(), new_name.c_str());
     code = ok ? 0 : errno;
 #endif
     return std::error_code(code, std::system_category());

src/common/util.h

@@ -145,7 +145,7 @@ namespace tools
   bool create_directories_if_necessary(const std::string& path);
   /*! \brief std::rename wrapper for nix and something strange for windows.
    */
-  std::error_code replace_file(const std::string& replacement_name, const std::string& replaced_name);
+  std::error_code replace_file(const std::string& old_name, const std::string& new_name);
 
   bool sanitize_locale();