fs/Path: rename to AllocatedPath

The new class Path only holds a string pointer without being
responsible for allocation/deallocation.  The FileSystem.hxx library
accepts Path arguments instead of AllocatedPath, to avoid forcing
callers to allocate another string object.

src/ConfigFile.cxx

@@ -253,7 +253,7 @@ ReadConfigFile(ConfigData &config_data, FILE *fp, Error &error)
 }
 
 bool
-ReadConfigFile(ConfigData &config_data, const Path &path, Error &error)
+ReadConfigFile(ConfigData &config_data, Path path, Error &error)
 {
 	assert(!path.IsNull());
 	const std::string path_utf8 = path.ToUTF8();