https://bz.apache.org/bugzilla/show_bug.cgi?id=62335

inspired by https://stackoverflow.com/questions/1170337/how-can-i-get-the-number-of-availableprocessors-in-ant

https://bz.apache.org/bugzilla/show_bug.cgi?id=62148

https://bz.apache.org/bugzilla/show_bug.cgi?id=62148

fixed by making the classloader used by checkForkedPath behave like a real forked classpath, thus completely isolated from the launching jvm

fixed by making the classloader used by checkForkedPath behave like a real forked classpath, thus completely isolated from the launching jvm

reverts a small part of 845c2c5

classes from ant-launcher.jar cannot load classes from ant.jar because
of the way we structure classloaders.

This reverts part of 66d7986