改进内容：
1. A new top level element, extension-point, allows build files to be extended with custom targets more easily.
2.
The "if" and "unless" attributes
will be evaluated according to the values of the properties entered if
these properties evaluate to true, false, on, or off.
3. Ant now requires Java 1.4 or later.
4.
A new task, include, provides an alternative to <import>
that should be preferred when you don't want to override any targets.
5. Numerous bugfixes and improvements were made.
下载地址： http://ant.apache.org/bindownload.cgi
