Fixed bug #10423 - GenericAgent: Invalid attributes can change job results.

Hi there,

i created a functionality to prevent the behavior described in my bugreport:

http://bugs.otrs.org/show_bug.cgi?id=10423

The attributes that have invalid values stored are marked with a warning text:
![bildschirmfoto 2014-03-31 um 17 28 12](https://cloud.githubusercontent.com/assets/3873515/2569146/cd1e4290-b8e9-11e3-9c14-db7499ab2d1d.png)
![bildschirmfoto 2014-03-31 um 17 28 22](https://cloud.githubusercontent.com/assets/3873515/2569147/cd1e3fd4-b8e9-11e3-8e6e-da5b33519985.png)

 In the case the user doesn't open the widget (to see these messages) a modal dialog pops up to inform the user:
![bildschirmfoto 2014-03-31 um 17 28 34](https://cloud.githubusercontent.com/assets/3873515/2569148/cd1f1e90-b8e9-11e3-9be1-4f748e36f08f.png)

Greetings, Thorsten

PS: The missing translations in the screenshots are caused by the framework.