Activate using "probes_buffer_size=60" in "szarp.cfg" to activate this
feature so that 10 second probes will be transfered to disk every
10 minutes.

WARNING: You will need to use pserver-lite (instead of probes_server)
to see current porbes (probes_server will only show data from disk).

This feature is a necessity when SZARP is working on vulnerable flash memory
types (ex. some types of SD-cards). Format of szbase is extremely disk
intensive (multiple 2-byte writes to same descriptor).

prober:
+ Connect to buffered probes segment.
+ Create snapshot of segment for *drift correction issues.
+ Correct +1/-1 *drifts.

*drifts: Drifts are caused inherently by parcook-prober communication
design which assumes that prober will reach for current probe
within 10-second window. This is not always true on embedded
systems suffering from heavy load. This issue is challenged by
this commit by means of optimisation of prober database writes
as well as buffering and active wait on prober side. Drift
fixing is of course a method of additional buffering that
allows to reach for past probes as wall as wait for probes
that are not yet here. Currently only +1/-1 cycle (10-seconds)
drifts are fixed but much greater drifts are actually fixable
by buffered snapshots (not yet implemented).

pserver-lite:
+ Check shared memory for probes that are not on disk but are expected.
+ Allow access to full range of probes (disk + shared memory).

meaner:
+ Optimise database writes (write probes in chunks - open file once).