Validate XML config files during the build

I took a look at the XmlLint task of Phing and think that it is not suited for the target we want to achieve here. Using the Phing task would require an additional XML Schema definition which is bad for two points:

1. For XJConf configuration files we already have the definitions in their own XML files. Adding schema definitions will double the amount of work when adding new tags.
2. XJConf configuration definitions can be extended by the user. We have no safe way of including guesses about this in our schema definitions.

As our XML files are mainly for XJConf I propose another solution:

1. All XJConf definition files and configuration files delivered as -dist files should be checked with integration tests as it is already done for the majority of this files.
2. Create a new Phing task that allows checking XJConf configuration files created by the user against the definition files by ensuring that reading the files with the appropriate classes delivered by Stubbles does not throw an exception.

Will probably not be implemented by me.

With r1395 a new base interface net::stubbles::lang::stubInitializer was introduced. Next step is to write a phing task that can execute a configurable list of net::stubbles::lang::stubInitializer instances.

Added a new task that executes a configured list of net::stubbles::lang::stubInitializer instances with r1397. Todo:

• rewort starwriter task to be compatible with stubInitClassLoader task in order to enable the new test-initializers target in the stubbles build file
• test new test-initializers target in release

The feature is now enabled with r1456. It still has to be tested within a release.

We will not support this for releases as the project structure of the application is somewhat hard to predict.