Correct the wrong prototype of fuse_daemonize(3) while retaining ABI compatibility

Increase the warning level to spot more mistakes

lib/librefuse: Implement FUSE session API and its signal handling functionality

lib/librefuse: Implement logging API appeared on FUSE 3.7

librefuse: Preparation of a proper API versioning; no more #ifdef woes in user code

The goal is to fully support FUSE API version 3.0 while maintaining
API/ABI compatibility with code written for 2.6 (or even older).

* <fuse.h> now emits a compiler warning if it's included without
defining FUSE_USE_VERSION. It had been silently defaulted to the
latest supported version prior to this change. This is permissive
compared to the original FUSE, as it emits an error instead.

* <fuse.h> now emits a warning if FUSE_USE_VERSION is higher than what
can be provided.

* Added a macro FUSE_MAKE_VERSION(maj, min). It was missing from
librefuse <fuse.h>.

No actual API updates have been made (yet).

fuse_lowlevel.h: new file, currently only contains fuse_parse_cmdline(3) and struct fuse_cmdline_opts

branches: 1.10.2;
Define _KERNTYPES for things that need it.

These directories default to WARNS?=5

branches: 1.8.28;
Header cleanup: don't need defs.h to do a few includes for us. Also,
use #include <> for global headers instead of #include "".

Get rid of MULTITHREADED_REFUSE for context queries. We can simply
use the pthread codepaths always.

branches: 1.6.4; 1.6.6;
get rid of DBG=

Add new Makefile knob, USE_FORT, which extends USE_SSP by turning on the
FORTIFY_SOURCE feature of libssp, thus checking the size of arguments to
various string and memory copy and set functions (as well as a few system
calls and other miscellany) where known at function entry. RedHat has
evidently built all "core system packages" with this option for some time.

This option should be used at the top of Makefiles (or Makefile.inc where
this is used for subdirectories) but after any setting of LIB.

This is only useful for userland code, and cannot be used in libc or in
any code which includes the libc internals, because it overrides certain
libc functions with macros. Some effort has been made to make USE_FORT=yes
work correctly for a full-system build by having the bsd.sys.mk logic
disable the feature where it should not be used (libc, libssp iteself,
the kernel) but no attempt has been made to build the entire system with
USE_FORT and doing so will doubtless expose numerous bugs and misfeatures.

Adjust the system build so that all programs and libraries that are setuid,
directly handle network data (including serial comm data), perform
authentication, or appear likely to have (or have a history of having)
data-driven bugs (e.g. file(1)) are built with USE_FORT=yes by default,
with the exception of libc, which cannot use USE_FORT and thus uses
only USE_SSP by default. Tested on i386 with no ill results; USE_FORT=no
per-directory or in a system build will disable if desired.

Hide struct puffs_usermount from the rest of the world and provide
accessors for interesting data in it. Namely, you can now get
pu->pu_privdata with puffs_getspecific(), pu->pu_pn_root with
puffs_set/getroot() and pu->pu_maxreqlen with puffs_getmaxreqlen().

* Move fuse_opt* defs and prototypes into fuse_opt.h.
* Move fuse_opt* funcs from refuse.c into refuse_opt.c.

Implement fuse_opt_parse() and fuse_opt_match(). And make the other
functions just dummy, always returning 0 (I added debugging printfs
to see what the application is trying to do).

For now there are two things that do not work in fuse_opt:

* options accepting arguments, i.e -otimeout=%u or -ofile=%s.
* options without arguments are not enabled, just parsed.

At least now curlftpfs works, even with verbose mode! :-)

Ok'ed by pooka.

LIBDPLIBS on puffs

Add an implementation of the file system in userspace functionality,
based on top of libpuffs. This version is still barebones and
incomplete, but will benefit from others working on it, rather than
just me.

The option code has still to be implemented, but this gets far enough
to run hellofs (from the fuse web page):

% priv ./hellofs ~/hellofs/mnt &
% l ~/hellofs/mnt
total 2
drwxr-xr-x 2 root wheel 0 Jan 1 1970 .
drwxr-xr-x 4 agc agc 512 Feb 9 18:05 ..
-r--r--r-- 1 root wheel 13 Jan 1 1970 hello
% cat ~/hellofs/mnt/hello
Hello World!
% df ~/hellofs/mnt
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/dk0 28101396 18946682 7749646 70% /
kernfs 1 1 0 100% /kern
procfs 4 4 0 100% /proc
ptyfs 1 1 0 100% /dev/pts
puffs:refuse:hellofs 28101396 18946682 7749646 70% /home/agc/hellofs/mnt
% mount -v -v
...
mount: mount_puffs not found for /home/agc/hellofs/mnt
puffs:refuse:hellofs on /home/agc/hellofs/mnt type puffs (nosuid, nodev, fsid: 0xcb01/0x6acb, reads: sync 0 async 0, writes: sync 0 async 0)
%

This code is not enabled by default. Yet.