Remove unused callback stubs.

They were just overridden a bit further down anyway
Give callbacks the current task they're working on

Without this additional parameter, log messages are confusing. The task
variable used in log messages would end up referencing the one from the
containing frame, which in this case is always the last one in the
assignment.
Fix a few log messages
Fix misleading doc string

map_path() will _not_ communicate with the master.
Bugfix: Use correct config keys in JobType.node()
Bugfix: Don't apply timedelta if not set
Merge pull request #138 from guidow/assign_bugfixes

Assign bugfixes