Alpha updated

[Brian Rice]

There are new images and VM sources uploaded to the alpha area. The  
VM contains important fixes and should be used.

New features:

- Greatly improved debugger - the debugger now is a real evaluator,  
and responds to various commands it installs on the implicit context  
(the lobby, mostly). Type "help." for the basic commands and see src/ 
lib/debugger.slate for details. (The interface right now is fairly  
basic and will get extended and probably cleaned up - suggestions  
welcome.)

- Resends with optionals were fixed.

- The `>> cascade macro was fixed for certain expansions involving  
the interaction between blocks.

- "a `swapWith: b" will swap the values of the two given variables  
transparently. They have to be variables in a block or method and not  
slots on the global tree.

I have also acquired a dual-G5 PowerMac system (I already use an  
iBook) and have verified that Slate compiles correctly for that  
architecture under GCC 3.3. GCC 4.0 compiles it without errors but  
there are some new warnings and the final output executable dies late  
in the process of bootstrapping the release images. I have also  
started learning about the new Tiger API's and will start working on  
some kind of (optional) Mac integration in the near future.

Enjoy!
-Brian