[plt-scheme] Trimming mzScheme

Hi,

I'm trying to reduce mzScheme to a lightweight implementation without any
references to platform specific instructions, so that I can embed it
easily.  (I don't need the Scheme interpreter to provide as much as
mzScheme does.)

There are two things that I'm finding problematic:

* Garbage Collection -- Is there any way to revert to a vanilla
implementation of a GC that does not use OS queries to isolate the stack?

* Thread support -- While mzScheme seems to implement it's own scheme
threads within the VM, what's the easiest way to make the application use
one thread only?


Thanks in advance.

Alex