Correctly pass argument vector as array during trustdb import/export/repair; fixes stale threads

Previously, stale threads were being left around, causing error messages to be written to stdout on exit, on account of the subprocesses intended to export and reimport the trustdb actually sitting around neither generating or consuming input. This happened on account of their command-line arguments being invalid (as a string -- a sequence of single characters -- rather than the expected list of valid arguments), and thus stripped.