LANG: new version of abstract syntax/translation document

Here is a new version of the document.

The only significant changes are in the introduction, where I have added a
list of non-closed issues that are addressed by the document.  (As I have
not been particularly well connected this week, the pointers in the
document don't point to the issue document yet.)  I don't expect any
changes except in response to comments for the next while.

I am still unhappy that this document anticipates so many resolutions that
have not yet been made.  I feel that this is putting the cart before the
horse, even though the feeling of the working group is becoming evident on
several of the open issues.  I feel that it would be a very good idea to
close issues that appear to have consensus, including 2.4, 3.4, 4.1 (which
is not even OPEN yet), 4.2 (which is not even OPEN yet), 5.2, 5.15, and
5.16.

peter