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Removed some unnecessary code and performed some cleanup on
tecodef.h.
Fixed VAXC definition of uintmax_t.
Add commets regarding radix constants.
Change IO_SUPPORT input callback to return the character, not a
status.  Internal IO errors are signalled by the handlers.
Updated to support the changes to the IO_SUPPORT input() callback.
Add ERROR macro.  This is the equivalent or ERROR_MESSAGE, without
specifying the name.
Fix up E file command support so that errors are returned appropriately.
Add support for EN command.