[CM] Multiple catch syntax

[bil at ccrma.Stanford.EDU]

catch uses eq? to match the tag to the error type --
I can't find any mention of this in s7.html -- will
make it explicit.  The expected usage for the
(or 'a 'b) case would be to have two catches.
Kinda ugly, now that I think about it. I borrowed
catch from Guile, and now I don't remember if they
accepted expressions for the tag.  I don't like
the r7rs "guard" or whatever they call it -- hmmm.