Save all values of non-static variables in this object in the file
'name'. valid_write() in the master object determines whether this is
allowed. The optional second argument is a bitfield: If bit 0 is 1,
then variables that are zero (0) are also saved (normally, they
aren't). Object variables always save as 0. If bit 1 is 1, then the
save file will be compressed.
If no file name is given (the argument is omitted or is the integer
flag bitfield), the serialized data is not written to disk but is
returned as a string instead, suitable for use with the string form of
restore_object().