Kawa externalizatio support checked in

[Per Bothner]

I checked in some changes, which turned out to be a more complex
than expected.  To summarize the visible changes:

Compliation of literals has been re-done.  A class that can be used
in a literal no longer needs to be declared as Compilable.  Instead,
you declare it as implementaing java.io.Externalizable, and make
sure it has appropriate methods.

All the standard "data" types (i.e. not procedures or ports) now
implement java.io.Externalizable, and can thus be serialized.
If they appear in literals, they can also be compiled.

The gnu.math package no longer has any dependencies on kawa.* or gnu.*.
-- 
	--Per Bothner
per@bothner.com   http://www.bothner.com/~per/