We bundle all required licenses and document the situation better in the
README.

We also make sure to bundle these licenses in our release archives.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@33676 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@159 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c