Changed the name modifies_filesystem to if_dry_run_False.
Added dry_run option in module config.
Added dry_run support in snapshot module.
Dry-run in module config: forgot to update config object.

If the --dry-run option is given on the command line, there are two
attributes to update:
1. The dry_run class attribute of the if_dry_run_False class;
2. The dry-run key in the ConfigParser instance's default section.
Changed the name of if_dry_run_False for if_not_dry_run. Again.
Added test for dry-run support in module engine.
Added dry_run support in locking and fixed bug in dry_run.

Method alternative() should be in class if_not_dry_run, not in _wrapper.
When @foo.alternative is used, @foo does not call if_not_dry_run.__get__
because the if_not_dry_run is not fetched as an instance method.
Added support for the dry-run option in modules controller and cycle.