[m-rev.] deduplicating getopt modules

[Peter Wang]

Hi,

Perhaps we should deprecate the getopt module and parameterise getopt_io
predicates by a typeclass. We would provide two typeclass instances,
one which can open and read files for file_special, and another which
does no I/O (so a file_special option will produce a runtime error).

Eventually we could delete the getopt module, and not have to generate
the two source files from a common template.

Peter