[9fans] read of eof

[Michael Baldwin <michael@cibernet.com>]

Obviously, a read of end-of-file should return -42. And if the data
is possessed, -666.

Seriously, there were two languages that I thought integrated
exceptions / failures well enough that you could actually use them
all the time pleasantly: Icon and Mesa. System calls (or expressions)
would "fail" instead of return in-band values, and the syntactic
sugar was light enough on calories that you didn't have the sense
that you were dragging out an exception handling harness with whipped
cream on top all the time just for one little call.

Ah well.