This can be easily fixed like this:
— build.xml (revision 507610)
+++ build.xml (working copy)
@@ -37,7 +37,7 @@
A nicer fix would be to also modify contrib/db to have ext-libs rather than lib (like gdata), but
for not holding 2.1 this is good enough I think.
Running "ant -Dversion=2.1.0 dist dist-src" like this and unpacking the src.zip, reults in
the same content as a clean "svn co" (except for the unwanted index.html").