MFC r296542:
Load linux64 module for amd64 if Linux abi enabled.

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

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

As previously discussed, add the svn:executable property to all scripts

Do not print anything unless at least one of the abi emulators is
enabled.

Eliminate global symbols starting with an underscore from rc.d
scripts, except for mdconfig* and jail. Such symbols are reserved
for the rc.subr internals. Most scripts can be fixed by just
declaring _foo symbols as local: few scripts actually need them to
be global.

Discussed with: dougb in freebsd-rc

Improve rc.d conformance:
- don't play a needless trick with prestart, just use start method;
- provide no-op stop method so that we don't get bogus "abi not running" error.

Set an example of using load_kld() from rc.subr.

Make sure abi (and therefore archdep) start before SERVERS as part of
the ongoing re-alignment of ordering that is necessary as a result of
including local scripts in the base rcorder. [1]

Accomplish this by removing the BEFORE's, and using REQUIRE instead.
This makes the dependencies more obvious, and less susceptible to turning
circular and/or nonsensical when seemingly innocent changes are made
in one place and not another.

Requested by: delphij [1]

As a quick fix disable the update of the linux ld.so.cache file, since
currently it grabs some FreeBSD native libs too.

A final solution is under discussion with brooks.

Be a little more read-only file system friendly when running the Linux
ldconfig. Build the cache in a temporary directory and only install it
if it's actually different that the installed one.

Also, use "cat tmp > real" to install the temporary file in the real
location to allow the real location to be a symlink to a writable
directory such as /var/run (where the file actually belongs).

MFC After: 5 days

Clear up problems with /etc/rc.d/{abi|cleanvar|cleartmp} brought
to light by the PR. Specifically, convert these three scripts
into good rc.d citizens, making sure that their functionality
is preserved, but the rc.d framework rules are not broken.

Add support for cleanvar as a regular rc.d script in the
default rc.conf, and document this in the man page.

Add a descriptive comment to rc.conf that regarding the
three emulation/compatibility services provided by abi
so users will not be confused by these services not having
their own startup scripts.

PR: conf/84574
Submitted by: Alexander Botero-Lowry

Remove the requirement for the FreeBSD keyword as it no longer
makes any sense.

Discussed with: dougb, brooks
MFC after: 3 days

Mark scripts as not usable inside a jail by adding keyword 'nojail'.

Some suggestions from: rwatson, Ruben de Groot <mail25@bzerk.org>

Move securelevel further back in the boot order.

Approved by: markm (mentor)(implicit)
Reviewed by: dougb

Merge in all the changes that Mike Makonnen has been maintaining for a
while. This is only the script pieces, the glue for the build comes next.

Submitted by: Mike Makonnen <makonnen@pacbell.net>
Reviewed by: silence on -current and -hackers
Prodded by: rwatson