run-id: Added implementation of run_id.

run_id is changed every time when syslog-ng is restarted but not when it is
reloaded. The actual value is stored in the persist file. A macro named RUNID
is available for using its value.
Merge pull request #60 from talien/f/runid

run-id: Added implementation of run_id.
lib/tests/Makefile.am: Clean up after test_run_id

Add test_run_id.persist- and test_run_id.persist to CLEANFILES. While
the second one should be automatically cleaned up by the test case, we
leave that in here too, for good measures. And make clean should clean
up after a failed test run, too, anyway.

Signed-off-by: Gergely Nagy <algernon@balabit.hu>