More updates for parallel process handling.

The source tests/test_g16.gpp now compiles and produces a working
program (prints 'X' on a line).
Assorted Guppy updates.

Some more work on parallel processes, operators and parsing.
Initial handling of external declarations.
More type and operator handling for Guppy.
Parser support for various Guppy language things.

This puts in place some of the language structure as proposed
previously.  Currently only tested up to the 'parse' compiler pass,
will not scope at present.
More updates for Guppy type handling.

Also added "oncreate" action for nodes, typically triggered when the
parser engine creates these.  Not called for tnode_copytree() derived
things.
Various Guppy type-system updates.
More updates for Guppy.

Starting to put some handling behind user-defined types.  Also added
the necessary stuff to handle array and record accesses in CCCSP output.
Added VARFREE to go with VARINIT on typedecls.

Assorted other small updates.