Hopefully fix some problems seen with MP support on non-x86, in particular
where curcpu() is defined as curlwp->l_cpu:

- mi_switch(): undo the ~2007ish optimisation to unlock curlwp before
calling

Hopefully fix some problems seen with MP support on non-x86, in particular
where curcpu() is defined as curlwp->l_cpu:

- mi_switch(): undo the ~2007ish optimisation to unlock curlwp before
calling cpu_switchto(). It's not safe to let other actors mess with the
LWP (in particular l->l_cpu) while it's still context switching. This
removes l->l_ctxswtch.

- Move the LP_RUNNING flag into l->l_flag and rename to LW_RUNNING since
it's now covered by the LWP's lock.

- Ditch lwp_exit_switchaway() and just call mi_switch() instead. Everything
is in cache anyway so it wasn't buying much by trying to avoid saving old
state. This means cpu_switchto() will never be called with prevlwp ==
NULL.

- Remove some KERNEL_LOCK handling which hasn't been needed for years.

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Don't play with "../.." in includes for h_macros.h; deal with it centrally.
Minor fixes.

more tests needing <sys/stat.h>

call previous with the correct args too

check that setuid() works for procs with >1 lwp

+ rump_lwproc_newproc -> rump_lwproc_rfork()
+ add a tess for rump_lwproc_rfork()

implicit pid is 1 instead of 0 now

+tc (turns out the bug was elsewhere, but a test is always a test)

check that curlwp for an implicit context is NULL

tests for rump_lwproc