Spec tweaks

I've posted "yet another spec" version of the formula work, as you can
see (and you can also see that the mailing list is back up!).

This has no changes in the BNF syntax from the previous one
for the rules that are used.  I say it in that way, because:
* I _did_ make a change in a rule that ISN'T used by the syntax,
   but is essentially a comment to clarify how to refer to a single cell.
   Now it's consistent with the REAL rule.
* The whitespace text was modified to clarify that whitespace is
   not allowed INSIDE the rule Identifier.  Well, okay, people probably
   already knew that, but best to make that clear...!
   Help clarifying the whitespace rules further would be great.

I added test cases for the syntax.  I realized while doing that,
that we need to make changes to the test template and environment.
To test for various syntactic cases, we need a "Sheet1" and "Sheet2"
with the test data, an external file 'openformula-testsuite.ods' with the
test data, and named expressions FOUR and ΔΩ to be assigned to
cell C4 (the name ΔΩ is used to test for support of international characters).

In case you're wondering, OOo happily handled ΔΩ exactly like it should;
I don't know about KOffice, but I bet they handle it already as well.
But even if they don't right now, I think that kind of i18n is very important.
It's critically important that users be able to give names in their
own language to named expressions; testing gives us confidence that
it really works.  Since we don't spec the UI, a PDA that doesn't
even HAVE international glyphs can show the ISO 10646 character codes
if it doesn't have a font to handle it.

The BNF still has the proposed optional prefix "$$" for names of
named expressions.

Lots of cleanups in various places, too.

--- David A. Wheeler