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/ClientFile.cxx

@@ -32,8 +32,7 @@
 #include <unistd.h>
 
 bool
-client_allow_file(const Client *client, const Path &path_fs,
-		  Error &error)
+client_allow_file(const Client *client, Path path_fs, Error &error)
 {
 #ifdef WIN32
 	(void)client;