GRADLE-571 - Introduced IsolatedAntBuilder which provides a builder style API for executing Ant tasks, identical to AntBuilder. - Simplified assembly of ClassLoaders in BootstrapMain, so that only a single ClassLoader is built containing logging + everything else. Simplifies life for embedders too. - No Gradle classes or libraries are visible to the ant+groovy versions used to execute the isolated build. - Cache and reuse ClassLoader for a given ant+groovy classpath.