Add tip to explain bad cage math

[GoogleCodeExporter]

In case a user enters a value which results in incorrect math for the cage a 
tip dialog should be shown to explain this issue.

Intended for:
 * Users who are not yet familiar with the rules of MathDoku.

Conditions for displaying:
 * Option "Mark bad maths" is enabled.
 * The "Do not show again" checkbox for this tip is not checked.

Optional functionality:
 * User who have already solved a game will be treated as an experienced player who already know the rules of MathDoku. The "Do not show again" checkbox for this tip will be checked when upgrading to this release.

Original issue reported on code.google.com by paul.din...@gmail.com on 1 Apr 2013 at 12:56

[GoogleCodeExporter]

This tip should also be displayed in case option "Mark bad math" is disabled.

Original comment by paul.din...@gmail.com on 18 Jul 2013 at 6:22

[GoogleCodeExporter]

This issue was closed by revision r402.

Original comment by paul.din...@gmail.com on 18 Jul 2013 at 7:18

• Changed state: Fixed

[GoogleCodeExporter]

Unfortunately the issue has not been verified explicitly by an independent 
tester.

Original comment by paul.din...@gmail.com on 8 Sep 2013 at 10:48

• Changed state: Verified