Use a seekless implementation of File:lines/love.filesystem.lines

The previous algorithm would seek every time. This meant that although reading
from a filesystem would be quick (especially with disk caching), but reading
from a zip would be extremely slow.

The new version is rouhgly as fast on a filesystem, but appears not to slow
down on zips at all. Not in my tests, at least.

--HG--
branch : minor

src/modules/filesystem/wrap_Filesystem.cpp

@@ -531,7 +531,9 @@ int w_lines(lua_State *L)
 	else
 		return luaL_argerror(L, 1, "expected filename.");
 
-	lua_pushcclosure(L, w_File_lines_i, 1);
+	lua_pushstring(L, ""); // buffer
+	lua_pushstring(L, 0); // buffer offset
+	lua_pushcclosure(L, w_File_lines_i, 3);
 	return 1;
 }