Remove duplicate file: blackbox_start
BIG CHANGES:
  * Command no longer need to be run from the base directory of the repo.
  * blackbox_edit now asks "are you sure?" and is greatly simplified.

_blackbox_common.sh:
  * add_filename_to_cryptlist now accepts paths relative to cwd.
  * fail_if_not_on_cryptlist now accepts paths relative to cwd.
  * new function: vcs_relative_path reports a path to the file relative to the REPOBASE.
  * new function: is_on_cryptlist

plus...
  * Some minor performance enhancesments and cleanups.
  * confidence_test.sh now tests some commands while not in REPOBASE.