Use gnuplot from buildout, and other small stuff

The main thing here is to use the gnuplot from buildout. Without 060b7b1a139a3450b389f8f539a0a2b62c8f7fec, the fl-build-report command fails because it can't find gnuplot.

c58d2bd5603176d17d148af0f0738c5a86d24109 serves to make this testable without having to re-run the benchmark.

665f735ffaa12d9725076454c2169e2f64ad744f makes sure that you can use this buildout without having to run a local server.

8feff30813114da6ceb09186bbfe2de2cfef0f7f is a small bugfix to the file location settings.