If MAKEDEFS_FILTER_NONASCII is defined (which config.h now does by
default), it will check data.base, rumors.*, and {various}.txt for
characters outside the range of ' ' through '~'. If it finds any, it
will warn about them and change them to '#'.
Tab handling is incomplete; the files that use tabs for indentation
will allow tabs anywhere, even though that's not wanted. That could
be fixed but doesn't seem particularly urgent. This is more about
spotting and repairing the special 3-char punctuation characters that
crept into data.base fairly recently.
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