The "ports" system provides functionality for porting pseudo to new targets.
The original motivation was a requirement to support older and newer Linux
systems on which the signature for clone() differed.

The Darwin port is totally nonfunctional at this point, but it compiles,
and sufficiently careful hand-tuning of DYLD_INSERT_LIBRARIES and a
manually-started server can actually pass a simple test.  It will get
worked on in my copious free time.

The basic design of a port is that it provides a wrapfuncs.in list of
function signatures, guts implementations, and optionally some port-specific
defines or a block of wrapper code for pseudo_wrappers.c.  This is used
for cases where the default wrapper would not be appropriate, and may
be combined with the new hand_wrapped=1 flag in wrapfuncs.in.

A port may specify preports or subports.  Preports are ports that are
included and processed *before* the current port -- meaning that functions
in the current port can override them.  Subports are processed *after*
the current port -- meaning that they can override functions in the
current port.  The preports and subports are specified by scripts,
which echo a list of port names to standard output.  (Be sure any
diagnostic messages go to standard error.)

