Cedar-backup3

* Fix ongoing problems re-initializing previously-written DVDs
- Even with -Z, growisofs sometimes wouldn't overwrite DVDs
- It turns out that this ONLY happens from cron, not from a terminal
- The solution is to use the undocumented option -use-the-force-luke=tty
- Also corrected dvdwriter to use option "-dry-run" not "--dry-run"

* Change writeIndicator() to raise exception on failure (closes 53).
* Change buildNormalizedPath() for leading "." so files won't be hidden
* Remove bogus usage of tempfile.NamedTemporaryFile in remote peer.
* Refactored some common action code into CedarBackup2.actions.util.
* Add unit tests for a variety of basic utility functions (closes: 45).
- Error-handling was improved in some utility methods
- Fundamentally, behavior should be unchanged
* Reimplement DVD capacity calculation (initial code from Dmitry Rutsky).
- This is now done using a growisofs dry run, without -Z
- The old dvd+rw-mediainfo method was unreliable on some systems
- Error-handling behavior on CdWriter was also tweaked for consistency
* Add code to check media before writing to it (closes: 5).
- Create new check_media store configuration option
- Implement new initialize action to initialize rewritable media
- Media is initialized by writing an initial session with media label
- The store action now always writes a media label as well
- Update user manual to discuss the new behavior
- Add unit tests for new configuration
* Implement an optimized media blanking strategy (closes: 48).
- When used, Cedar Backup will only blank media when it runs out of space
- Initial implementation and manual text provided by Dmitry Rutsky
- Add new blanking_behavior store configuration options
- Update user manual to document options and discuss usage
- Add unit tests for new configuration

* Fix typo in new split section in the user manual.
* Fix incorrect call to new writeIndicatorFile() function in stage action.
* Add notes in manual on how to find gpg and split commands.

* Fix some encrypt unit tests related to config validation
* Make util.PathResolverSingleton a new-style class (i.e. inherit from object)
* Modify util.changeOwnership() to be a no-op for None user or group
* Created new split extension to split large staged files.
- Refactored common action utility code into actions/util.py.
- Update standard actions, cback-span, and encrypt to use refactored code
- Updated user manual to document the new extension and restore process.

* Fix log message about SCSI id in writers/dvdwriter.py.
* Remove TODO from public distribution (use Bugzilla instead).
* Minor changes to mbox functionality (refactoring, test cleanup).
* Fix bug in knapsack implementation, masked by poor test suite.
* Fix filesystem unit tests that had typos in them and wouldn't work
* Reorg user manual to move command-line tools to own chapter (closes: 33)
* Add validation for duplicate peer and extension names (closes: 37, 38).
* Implement new cback-span command-line tool (closes: 51).
- Create new util/cback-span script and CedarBackup2.tools package
- Implement guts of script in CedarBackup2/tools/span.py
- Add new BackupFileList.generateSpan() method and tests
- Refactor other util and filesystem code to make things work
- Add new section in user manual to discuss new command
* Rework validation requiring least one item to collect (closes: 34).
- This is no longer a validation error at the configuration level
- Instead, the collect action itself will enforce the rule when it is run
* Support a <no_eject> flag in store configuration (closes: 39).
- Change StoreConfig, CdWriter and DvdWriter to accept new flag
- Update user manual to document new flag, along with warnings about it
* Support repository directories in Subversion extension (closes: 46).
- Add <repository_dir> configuration modeled after <mbox_dir>
- Make <type> configuration value optional and for reference only
- Refactor code and deprecate BDBRepository and FSFSRepository
- Update user manual to reflect new functionality

* Fix a few places that still referred only to CD/CD-RW.
* Fix typo in definition of actions.constants.DIGEST_EXTENSION.