word breaks and control-a

[haahr@mv.us.adobe.com (Paul Haahr)]

[Noah makes some very good points about backwards compatibility
and why it can be a bad thing.]

> Why not also fix the same bug in rc?

no reason not to, i guess.  people are sometimes hesitant to upgrade,
but that's not a convincing reason.

if we do change this, though, my preference is the ``backwards
compatible'' way i outlined before, because it does not depend
on a synchronized (``flag day'') release between rc and es.
the additional cost in terms of lost valid sequences (^b^a and
^b^a) is truly minimal.

when exporting, the following mapping would occur

	word break	-> ^a
	^a		-> ^b^a
	^b		-> ^b^b

and when importing

	^a		-> word break
	^b^a		-> ^a
	^b^b		-> ^b
	^bx		-> ^bx		# where x is anything else

so now the bugs section comment should be

	Woe betide the environment string containing the character control-a
	or the sequence control-b followed by control-a or control-b.

i propose making this change in es, independent of what happens to rc.

paul