ensure that we only drop our self-reference exactly once.

To maintain the guarantee that an object won't go out of scope
unexpectedly while one of its event handlers is being called, the
event-calling functions now automatically obtain and drop extra
references.

functions.

Add "xfer" to all xfer functions and "job" to all job functions.

the most generally useful way.

in code defining reference-counted objects.

Dehyphenate "data-transfer".

functions.

output buffering defintions and the like)

connections might break things. Only-sending applications like syslog()
do not need a newdata() handler, so added a check if that handler exists.

Generate DHCP data block for images.

block, so first32.c dies immediately.

image file.

ISA 3c509 is currently non-functional, although the EISA (3c509-eisa) and
MCA (3c529) variants should build OK.

None of this code is yet tested.