cpdb-backend-file 2.0b4

In the forth beta release for cpdb-backend-file 2.0.0 we have now added a make check test and fixed a crasher.

• Added test script for make test/make check
  The script src/run-tests.sh starts this backend and the cpdb-text-frontend text mode example frontend of cpdb-libs in one dbus-run-session environment. The frontend discovers the backend and some test tasks are done with it, like listing options and printing a job.
• README.md: Updated for renaming of cpdb-libs tools
  The test/development frontend print_frontend is renamed to cpdb-text-frontend now.
• Fixed buffer overflow caused in log line in the backend