Big changes to make Base and some others work in Mozart 2.

This commit is actually a manual merge of the code we wrote by
bits for Mozart2. That history is not included here because the
branches were in two separate repos with no common ancestor commit.
It's just safer not to introduce multiple roots in this repo.

The history of these commits is still available in the main repo.
The code that is now here was located under directory lib/.

base/Atom.oz

@@ -26,5 +26,19 @@
 %%
 %% Module
 %%
-Atom = atom(is:       IsAtom
-            toString: AtomToString)
+
+fun {AtomToUnicodeString A}
+   if {IsAtom A} then
+      {VirtualString.toUnicodeString A}
+   else
+      raise typeError('Atom' A) end
+   end
+end
+
+fun {AtomToString A}
+   {UnicodeString.toString {AtomToUnicodeString A}}
+end
+
+Atom = atom(is:              IsAtom
+            toUnicodeString: AtomToUnicodeString
+            toString:        AtomToString)