Previously, this code would raise the following exception if file it was trying
to read did not exist. The `datafile` variable would never be set.
File ".virtualenvs/taskotron/bin/runtask", line 9, in <module>
load_entry_point('libtaskotron==0.0.3', 'console_scripts', 'runtask')()
File "devel/libtaskotron/libtaskotron/runner.py", line 131, in main
task_data = taskyaml.parse_yaml_from_file(arg_data['taskfile'])
File "devel/libtaskotron/libtaskotron/taskyaml.py", line 9, in parse_yaml_from_file
datafile.close()UnboundLocalError: local variable 'datafile' referenced before assignment