Add comment explaining one of the quirks in autofs.

MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Autofs softc needs to be global anyway, so don't pass it as a local
variable, and don't store in autofs_mount.  Also rename it from 'sc'
to 'autofs_softc', since it's global and extern.

MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
vt(4): Fix cursor handling in vt_flush()

There were situations where the cursor was not erased/redrawn or its
position was marked as dirty even though it's not displayed. The code is
now more straightforward.

At the same, add a function to determine if the cursor covers a given
area. This is used by backends to know if they need to draw the cursor.

This new function should be paired with a new state in struct vt_device,
called vd_mshown, which indicates if the cursor should be displayed.
This again simplifies vd_bitblt_text_t callback's API.

MFC after:	1 week
Don't fail on executable maps that return no entries.  This turns useless
error message into useful one.

MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Add "nobrowse" option.  Previously automountd(8) always behaved as if
it was set, now it's conditional.

PR:		192862
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation