Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Update the rest of struct ithd references.
- net_ih and softclock_ih cookies have gone away.

MFC after: 1 week

Document swi_remove(9).

Reviewed by: jhb
MFC after: 1 week

Update the swi_add prototype after struct ithd was split up into
struct intr_event and struct intr_thread.

PR: docs/166864
Reviewed by: jhb (older version)
MFC after: 1 week

Retire the INTR_FAST flag as it was obsoleted by the introduction of the
filter argument to bus_setup_intr().

Make an argument name in the synopsis match that in the text. Correct
an mdoc error.

Tabs here upset my automatic checker, so replaced them with spaces.

mdoc(7): Use the new feature of the .In macro.

mdoc(7) police: scheduled sweep.

Approved by: re

SWI_SWITCH and SWI_NOSWITCH were OBE a long time ago.

Typo: s/conjuction/conjunction/

mdoc(7) police: Use the new .In macro for #include statements.

mdoc(7) police: Use Vt for variable types.

Catch up to the new swi API.

Fixed missing and/or wrong and/or extra includes in synopsis.

mdoc(7) police: Ft/Vt now accept punctuation-type arguments.

Prepare for mdoc(7)NG.

Add a newline character at the end of this file, it was missing which
resulted in ugly errors from 'diff'.

Describe the new software interrupt thread functionality.

Reviewed by: sheldonh, jasone