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/StickerDatabase.cxx

@@ -107,13 +107,11 @@ sticker_prepare(const char *sql, Error &error)
 }
 
 bool
-sticker_global_init(Path &&path, Error &error)
+sticker_global_init(Path path, Error &error)
 {
-	int ret;
+	assert(!path.IsNull());
 
-	if (path.IsNull())
-		/* not configured */
-		return true;
+	int ret;
 
 	/* open/create the sqlite database */