fix pad file bug in create_torrent and amend docs about pad files

docs/make_torrent.rst

@@ -319,7 +319,8 @@ piece_size will be calculated such that the torrent file is roughly 40 kB.
 If a ``pad_size_limit`` is specified (other than -1), any file larger than
 the specified number of bytes will be preceeded by a pad file to align it
 with the start of a piece. The pad_file_limit is ignored unless the
-``optimize`` flag is passed.
+``optimize`` flag is passed. Typically it doesn't make sense to set this
+any lower than 4kiB.
 
 The overload that takes a ``torrent_info`` object will make a verbatim
 copy of its info dictionary (to preserve the info-hash). The copy of

src/file_storage.cpp

@@ -540,7 +540,8 @@ namespace libtorrent
 				i->offset = off;
 				char name[30];
 				snprintf(name, sizeof(name), ".____padding_file/%d", padding_file);
-				i->set_name(name);
+				std::string path = combine_path(m_name, name);
+				i->set_name(path.c_str());
 				i->pad_file = true;
 				off += pad_size;
 				++padding_file;