Create deprecation management functions.

[imp]

Summary

gone_in(majar, msg); If we're running in FreeBSD major, tell

			the user this code may be deleted soon.
			If we're running in FreeBSD major - 1,
			the the user is deprecated and will
			be gone in major.
			Otherwise say nothing.

gone_in_dev(dev, major, msg) Just like gone_in, except use device_printf.

New tunable / sysctl debug.oboslete_panic: 0 - don't panic,
1 - panic in major or newer , 2 - panic in major - 1 or newer
default: 0

if NO_OBSOLETE_CODE is defined, then both of these turn into compile
time errors when building for major. Add options NO_OBSOLETE_CODE to
kernel build system.

This lets us tag code that's going away so users know it will be gone,
as well as automatically manage things.

[rpokala]

And of course the same comments for _gone_in_dev() as in _gone_in().

sys/kern/subr_bus.c

5608

"Manage deprecated / obsolete code."

5632

Use P_OSREL_MAJOR() rather than doing it by hand.

5636

The "running" seems... not right. "Obsolete code; will be removed soon" sounds better to me.

sys/sys/systm.h

468

"API for managing deprecated / obsolete code."

[rpokala]

sys/kern/subr_bus.c

5632

For that matter, shouldn't m be a static variable (or a #define) outside of the scope of either of these functions, since it's a constant value used by both of them?

[imp]

Tag drivers