Fixes issue #64:

[owenca]

Only allow decimal digits 0-9 in the text control for the Size test.

[humdingerb]

I found one problem:
The disallowing of non-digits in the "Size" text control works when creating a new rule or editing a rule the first time after Filer is launched. But after that, editing a rule does again allow non-digits. The value with the non-digits also gets saved with the rule.

And: could you title your PRs more detailed in the future, please. "Fixes #64" isn't very helpful when someone looks over a list of commits. Maybe "Disallow non-digits in size test (issue #64)", then add more info in the body of the commit message if you'd like to explain further, or simply add "Fixes issue #64." if it's all obvious.

[owenca]

Sorry that I forgot a list of commits would only show the first line of the commit message. I will update it when updating the commit to fix the bug you found.

[owenca]

Fixed.

[humdingerb]

Works! Thanks very much.