This patch displays a warning to the user in two cases:
1. When special files like symlinks, fifos, devices, etc. are found in the
local source.
2. If files or directories are not readables by the user running the 'tahoe
backup' command.
In verbose mode, the number of skipped files and directories is printed at the
end of the backup.
Exit status returned by 'tahoe backup':
- 0 everything went fine
- 1 the backup failed
- 2 files were skipped during the backup
* backups now share dirnodes with any previous backup, in any location,
so renames and moves are handled very efficiently
* "tahoe backup" no longer bothers reading the previous snapshot
* if you switch grids, you should delete ~/.tahoe/private/backupdb.sqlite,
to force new uploads of all files and directories
* emit lease expiry date in ISO-8601'ish format as well as Brian's format
* rename iso_utc_time_to_localseconds() to iso_utc_time_to_seconds()
* add iso_utc_date()
* simplify the body of iso_utc_time_to_seconds()
