#13 patching/modification and incremental building

[Sergey Vorobyev]

We use daCapo benchmark in open source java race detector develop process.
I fix your ant build scripts and now I can change apache tomcat source and it doesn't override.
I often make minor changes and exec 'ant tomcat'.
Build process take about 10 min.

I think it's good idea and useful for developers allow patching/modification and/or incremental building.