Use system scala and CLASSPATH for packages.

Change-Id: I4f175505860d6e910e0e7bc34f9dd5861939cbb8
configure.ac: improve handling of pencil tools

Before, configure would fail with

  checking for ""... no

when it could not find the PENCIL optimizer or linker.

Change-Id: I79caee94faf0577560a5ee90199b855fbbd6ea64