Make doit aware of runbk.
Make doit aware of runbk.

In a runbk environment, the bk binary from that will be used instead
of the one in the source tree the tests are run from.

bk: 4964d7a5r9OZP3xuMZzaZnw-wFwAYg
bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper,bitkeeper-scm/bitkeeper