Rxnpatch: Support multiple revisions of clusters.

Prepares for fixing [bug 7225].
Rxnpatch: Support creation of multiple clusters on the same day.

If a cluster already exists, a revision number will be appended
to the timestamp (starting with "-02") to make it unique.

Fixes [bug 7225].
Rxnpatch: Added some cluster creation paranoia.

Cluster creation now aborts (instead of making an invalid tar file)
if a contained filename is too long (ie 100 characters or more).
This is unlikely to ever happen, but...
Merge branch 'grubba/patchsystem' into 5.4

* grubba/patchsystem:
  Rxnpatch: Added some cluster creation paranoia.
  Rxnpatch: Support creation of multiple clusters on the same day.
  Rxnpatch: Support multiple revisions of clusters.
Enable execution of FTP requests in handler threads by -DFTP_USE_HANDLER_THREADS.

Conflicts:
	.gitattributes
Debug: Moved gc histograms to a separate debug flag.

The gc histograms are now enabled with -DLOG_GC_HISTOGRAMS
(or -DLOG_GC_VERBOSE).

Fixes [bug 7197].
Merge branch 'grubba/gc-logging' into 5.4

* grubba/gc-logging:
  Debug: Moved gc histograms to a separate debug flag.