Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Move MINSIGSTKSZ from <machine/signal.h> to <machine/_limits.h> and rename
it to __MINSIGSTKSZ. Define MINSIGSTKSZ in <sys/signal.h>.

This is done in order to use MINSIGSTKSZ for the macro PTHREAD_STACK_MIN
in <pthread.h> (soon <limits.h>) without having to include the whole
<sys/signal.h> header.

Discussed with: bde

Start all license statements with /*-

Remove the empty definition of struct osigcontext, as it will never be used.

Don't declare osigset_t, as it is done in sys/_sigset.h.

Remove advertising clause from University of California Regent's license,
per letter dated July 22, 1999.

Approved by: core

Add standards visibility conditionals. Change any uses of sigset_t to
struct __sigset to avoid depending on objects from <sys/signal.h>.

We need machine/{signal,ucontext}.h to build a cross GCC compiler.
So craft the proper versions of these and commit em.