For the ant target download-cpachecker,
extract only the JAR file from the downloaded archive,
and use ivy to download the libraries.
Ivy uses local caching and is able to restore the original file
timestamps, allowing the VerifierCloud client to use cached hash codes.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13563 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c