Feature dry run

Hello,

-------------------
This patch adds an option --dry-run to the run command.

In this mode changes to the database are prevented by a thin
layer around the the database object. Task action and teardown
execution is skipped.
-------------------

I did not test it thoroughly, its my first contribution :-). I did not add tests for the new code. Do you think this can be pulled ? Or what do you require for it being pulled ?


Thanks for your efforts,
Oliver
My mistake. I meant to query teardowns as well. I would change 
'runner.py:execute_task' that they are queued and printed also in 
dry-run mode. What do you think ?

Am 02.11.2014 um 00:50 schrieb eduardo naufel schettino:
> In doit/runner.py:
>
>> @@ -208,7 +213,9 @@ def teardown(self):
>>          """run teardown from all tasks"""
>>          for task in reversed(self.teardown_list):
>>              self.reporter.teardown_task(task)
>> -            catched = task.execute_teardown(sys.stdout, sys.stderr,
>> +            catched = None
>> +            if not self.dry_run:
>
> I guess this change wont be needed because teardown_list will always be
> empty on dry_run mode.
>
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> <https://github.com/pydoit/doit/pull/10/files#r19708739>.
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