warn/croak on "string" "string" auto-joins

[Robert Dewar]

The latest post on this thread had 7 levels of nested
quotes. This business of casually quoting the entire
message results in a quadratic accumulation of junk.
We really don't need the whole thread in every message.
It would be nice if people were a little bit more
selective in quotations. The message in question
by the way, after quoting over a hundred lines of
text with 7 levels of quotes, adds precisely three
lines of original text.