VFS: make m_in job local

By making m_in job local (i.e., each job has its own copy of m_in instead
of refering to the global m_in) we don't have to store and restore m_in
on every thread yield. This reduces overhead. Moreover, remove the
assumption that m_in is preserved. Do_XXX functions have to copy the
system call parameters as soon as possible and only pass those copies to
other functions.

Furthermore, this patch cleans up some code and uses better types in a lot
of places.
VFS: find job only if request is an transaction
libmthread: add stack traces
VFS: enable sending control messages
Add a simple utility to send control messages

The svrctl utility allows you to send control messages to VFS or PM.
This way you can retrieve runtime information or alter behavior.
VFS: warnings are errors
VFS: fix new signed/unsigned comparisons
VFS: fix dead lock

When running out of worker threads to handle device replies a dead
lock resolver thread is used. However, it was only used for FS
endpoints; it is now used for "system processes" (drivers and FS
endpoints). Also, drivers were marked as system process when they
were not "forced" to map (i.e., mapping was done before endpoint was
alive).
VFS: let know when skipping reply
VFS: remove debug print
VFS: add getting active threads control msg
TTY: don't allow multiple readers on tty minor

TTY has no way of keeping track of multiple readers for a tty minor
device. Instead, it stores a read request for the last reader only.
Consequently, the first ("overwritten") reader gets stuck on a read
request that's never going to be finished. Also, the overwriting
causes a grant mismatch in VFS when TTY returns a reply for the
second reader.

This patch is a work around for the actual problem (i.e., keeping track
of multiple readers). It checks whether there is a read operation in
progress and returns an error if it is --preventing that reader from
getting overwritten and stuck. It fixes a bug triggered by executing
'top | more' and pressing the space bar for a while (easily reproducable
in a VM, not on hardware).
VFS: more three-level-lock sanity checking
VFS: fix filp reuse race

Pipes consist of two filps (read filp and write filp) and a shared
vnode. When the writer leaves the filp reference count drops to
zero and subsequent find_filp()s should not find the filp when a
reader looks for it and the reader gets EOF. However, the pipe()
system call tries to find two filps, marks them in use, and only
after a successful node creation on PFS, overwrites the shared
vnode with the new vnode. Consequently, this leaves a small window
where a just closed 'pipe write filp' gets reused and marked as
present, before becoming the actual new 'pipe write filp' for a new
pipe. A reader for the old pipe will think a writer is present and
wait for that writer to write something or to leave; both actions
should revive the suspended reader. This will never happen and the
reader will be stuck forever.
service: make clear who is printing the error
Fix booting into single user mode

Due to a shift, mountfstab was unable to locate the fstab file and
mount other file systems causing a number of errors to be generated.
Provide boot option to boot into single user mode
kernel: align gdt and idt base addresses

patch my fdmanana:
As recommended by the Intel 64 and IA-32 Architectures Developer's
Manual Volume 3A, the GDT and IDT base addresses should be aligned on an
8 byte boundary to yield better processor performance.
recognize and execute dynamically linked executables

  	. generalize libexec slightly to get some more necessary information
	  from ELF files, e.g. the interpreter
	. execute dynamically linked executables when exec()ed by VFS
	. switch to netbsd variant of elf32.h exclusively, solves some
	  conflicting headers
build shared versions of libraries

building defaults to off until clang is updated.

current clang does not handle -shared, necessary to change the ld
invocation to build shared libraries properly. a new clang should be
installed and MKPIC defaults to no unless the newer clang is detected.

changes:

	. mainly small imports of a Makefile or two and small fixes
	  (turning things back on that were turned off in Makefiles)
	. e.g.: dynamic librefuse now depends on dynamic
	  libpuffs, so libpuffs has to be built dynamically too
	  and a make dependency barrier is needed in lib/Makefile
	. all library objects now have a PIC (for .so) and non-PIC
	  version, so everything is built twice.
	. generate PIC versions of the compat (un-RENAMEd) jump files,
	  include function type annotation in generated assembly
	. build progs with -static by default for now
	. also build ld.elf_so
	. also import NetBSD ldd