Build error if using a different xsd target directory than the configured meta-inf directory.

This is an issue when using the xbean maven plugin but also the generator task in xbean-blueprint.

Normally the generated XSDs are put into the root of an artifact which is obviously the location where the META-INF directory resides. When the DocumentGenerator (I think it's called) is executed during the build, it tries to generate the HTML documentation in the location where the xsd is going to be generated. If the xsd is configured to be generated in a path that doesn't exist by default, such as the target/classes directory, then the html file cannot be generated because that xsd path doesn't exist yet. When the xsd is generated, if the directory that is specified doesn't exist, it's created. This happens after the DocumentGenerator is configured to run. So making sure the directory is created if it doesn't exist, corrects this problem. I think the same fix needs to be applied to the xbean-spring equivalent classes, which I didn't include in my pull request.

The "Different dirs fix" pull request I submitted has changes to fix this issue in xbean-blueprint. Ignore the two commits that aren't mine, I'm not sure how I caused them to be in there. I had to create a branch and add in the proper commits for the pull request, everything needed should be there for it, I apologize if I goofed, if anything is missing let me know and I'll give you whatever it is