Revision 1505063

Using <antversion> condition to check for Ant at least version 1.7.0
(instead of using string tests for each supported version).

This is a little problematic since the <antversion> condition was
introduced in Ant 1.7 (i.e., version 1.6 will fail in a rather ugly
fashion).  But, everyone should be running recent versions anyway,
since 1.7 was released in December 2006.

This is a merge of revision 1505062 from branches/2.0.x to trunk.