Fixed some bugs in settings_object handling and got test_usage.sh working.

Highlights:
  * clarified settings_object handling and improved unittests
  * added `be list --mine`
  * fixed some bugs in List, Import_XML, Init
  * added Storage.exists() (haven't implemented it in all VCS backends though).
  * added VCS.path()

diff --cc NEWS
index 17d5aee88d4188132d53b1697f3b3da009e9204b,17d5aee88d4188132d53b1697f3b3da009e9204b..e0dc81caba9cb52ec7016ee705945343f2e43875
--- 1/NEWS
--- 2/NEWS
+++ b/NEWS
@@@ -1,3 -1,3 +1,6 @@@
++January 23, 2010
++ * Added `be list --mine`, listing bugs belonging to you.
++
  January 20, 2010
   * Renamed 'be-mbox-to-xml' -> 'be-mail-to-xml' and added support for
     several mailbox formats.