* signal handling
  - SIGINT should be handled gracefully.

* svk diff
  - use tmp files and libsvn_diff's output_diff function instead of non-streamy Text::Diff.

* better tree merger
  - Merge added directories.
  - Merge moved files and directories.

* properties
  - Support svn:eol-style.
  - Support svn:special.

* checkout maintenance
  - move checkouts.
  - purge dead checkouts.

* checkout signatures
  - command to purge cache.
  - cache for modified files also, but the gain is marginal.

* finalize SVK::Patch interface
