Option for value labeled values

[matthew-white]

Add an option specifying that the new values variable may contain value label text. In terms of the auto dataset, right now replacements for variable foreign would require a replacements file like this:

make	Variable	Value
Plym. Volare	foreign	1
VW Diesel	foreign	0
VW Rabbit	foreign	0

However, it'd be great if value label text (Domestic/Foreign) could be listed instead of/in addition to values (0/1):

make	Variable	Value
Plym. Volare	foreign	Foreign
VW Diesel	foreign	Domestic
VW Rabbit	foreign	Domestic