Support non-blocking reads from USB printers. With this, escputil can
query the printer model, and I can print a test page with gutenprint
5.1 and cups. Add many comments explaining why the support is not
quite right. (This change is quite a bit less invasive than a
"correct" fix, and thus more reasonable to pull up to netbsd-4.)
Rototill debugging, so that all DPRINTFN have a level, and so that the
message is printed if the debug level is >= the number in the source
code. Document debug level plan.
Fix bug where only one status change would be printed (by inspection,
not tested).
Document scheme for reading/discarding data when ulpt(4) is opened for
write only.
Delete dead code.
Plan and patch posted on tech-kern without objections.
1424adf410