[gclist] New gc versions

[Boehm, Hans]

I made available two new versions of our garbage collector:

5.3: Version 5.2 with some bug fixes.  5.3 should work much better as a leak
detector.

6.0alpha3: Derived from 6.0alpha2, but significantly reorganized.  Fixed a
significant performance bug in the parallel marking algorithm, and several
correctness bugs all over the place.  Appears to work at least under Linux
(X86 and IA64, with parallel marking etc.) and under Windows and HP/UX
(wihout ...).  Should be much better than alpha2.

Details are in
http://www.hpl.hp.com/personal/Hans_Boehm/gc/gc_source/recent_changes

The code is in http://www.hpl.hp.com/personal/Hans_Boehm/gc/gc_source/ ,
description is at http://www.hpl.hp.com/personal/Hans_Boehm/gc/ , also as
usual.

Hans