Bring in various fixes from FreeBSD:

Bring in various fixes from FreeBSD:

* MAXPATHLEN includes the trailing NUL, Correct array sizes to reflect this.
* Correct NUL termination after strncpy.
* Make ${.OBJDIR} canonical.
* -Wall cleanup.
* unifdef -D__STDC__
* Sort #includes, remove <sys/types.h> (made redundant by <sys/param.h>),
  add <signal.h> (needed for sigaction())
* Unbreak compilation on RELENG_4.
* unifdef -UWANT_ENV_PWD. No one ever going to use this bugfeature.
* Reorder #include. Cast arg #2 of lseek to an off_t when constant. No need to
  test if failsafe memory allocation fails, it can't. perror -> warn. Use
  failsafe memory allocation provided.
* And some other doc cleanup.
* Reduce diffs between FreeBSD and DragonFly Makefile
* Added the MAKE_VERSION global that could be useful in determining
  if a given make(1) is feature-compatible with a set of makefiles.
  When merged, this will be used to replace the ugly upgrade_checks
  hacks in src/Makefile.
  Version has the RYYYYMMDDX format, where R is from RELENG_<R> and
  X allows for 10 distinguishable changes per day.
* make(I) appeared in PWB UNIX.
* Add MAKE_VERSION variables
* Don't do stupid things to avoid unused parameters, mark them __unused.
* Use %p to print a pointer, not %lx and a cast to (unsigned long).  Yuck.
* Avoid classy use of a variable one time with a constant value.
* Bit-width fields should be of type 'int'.

Submitted-by: Max Okumoto <okumoto@home>