etc: force system.conf install

Change-Id: I5f88b108248fb3cee457de8a2f2baa2f30b0a335
mkfs.mfs fixup

 For the special case of crossbuilding minix on minix.
some etc fixes

	. split user-editable and system-owned files in etc/Makefile
	. mtab is a symlink, not a file now; remove it
	. force-install of certain system-controlled /etc files from
	  top Makefile
	. rename /etc/make.conf to /etc/mk.conf; and don't set $ARCH;
	  reduce difference in bsd.own.mk

Change-Id: I9f4bbb8d37ba80cba7dcfcf1a9a89e934910f579
kernel: rename realtime to monotonic, add realtime

Old realtime was used for both timers (where an accurate count of
all ticks is needed) and the system time. In order to implement
adjtime(2), these duties must be separated as changing the time
of day by a small amount shouldn't affect timers in any way nor
should it change the boot time.

Following the naming of the clocks used by clock_gettime(2). The
clock named 'realtime' will represent the best guess at the
current wall clock time, and the clock named 'monotonic' will
represent the absolute time the system has been running.
Use monotonic for timers in kernel and in drivers. Use realtime
for determining time of day, dates, etc.

This commit simply renames realtime to monotonic and adds a new
tick counter named realtime. There are no functional changes in
this commit. It just lays the foundation for future work.
libc: add clock_getres()/clock_gettime() system calls.

In order to make it more clear that ticks should be used for timers
and realtime should be used for timestamps / displaying the date/time,
getuptime() was renamed to getticks() and getuptime2() was renamed to
getuptime().

Servers, drivers, libraries, tests, etc that use getuptime()/getuptime2()
have been updated. In instances where a realtime was calculated, the
calculation was changed to use realtime.

System calls clock_getres() and clock_gettime() were added to PM/libc.
test69: add clock_getres() and clock_gettime() tests.
libc: add clock_settime() system call.

This also adds the sys_settime() kernel call which allows for the adjusting
of the clock named realtime in the kernel. The existing sys_stime()
function is still needed for a separate job (setting the boottime). The
boottime is set in the readclock driver. The sys_settime() interface is
meant to be flexible and will support both clock_settime() and adjtime()
when adjtime() is implemented later.

settimeofday() was adjusted to use the clock_settime() interface.

One side note discovered during testing: uptime(1) (part of the last(1)),
uses wtmp to determine boottime (not Minix's times(2)). This leads `uptime`
to report odd results when you set the time to a time prior to boottime.
This isn't a new bug introduced by my changes. It's been there for a while.