Introduce progress output for fast cluster to cluster transfer (bb#709)

Change sxi_cluster_query function to be a wrapper of
sxi_cluster_query_track. Now xfer_stat structure is passed to struct
generic_ctx context to enable progress tracking for generic
transfers too. This is done if track_xfer parameter is set to positive
though.

Update sxcp tool to fit both direction transfers.
respect debug mode when going verbose (bb#728)
cache api rework
return file revisions in listfiles, do not return random crap for dirs
check revision presence in tests
make file lists cachable
drop useless dead code
temporary workaround sxls to support old servers
Use time window for ETA computation

Keep information about current transfer speed in time window to properly
estimate finish time.

sxcp progress handling cosmetics (braces && indentation).
Code cosmetics

Prevent progress bar flashing when frequent transfer changes occur. This
is mainly applicable on resumes and transfer retries.

Change indentation.
Silence compiler warnings.
Change few local variables types from int to unsigned int that are used as array indices. That stops warnings about comparing signed and unsigned variables.
Print progress information to stderr instead of stdout

Summaries are printed to stdout