Add a vsnprintf() for the Mac, which doesn't have one of its own. This is

Add a vsnprintf() for the Mac, which doesn't have one of its own.  This is
the NetBSD kernel printf, which is integer-only and under a Berkeley-style
(now 3-clause) copyright owned by UCB.  This has only been compile-tested,
but almost all of my changes were in the definitions at the top (the exception
being to remove tty output).  This lacks 64-bit support because the Apple
68K C compiler, SC, lacks it too.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2451 cda61777-01e9-0310-a592-d414129be87e