allow dbunit maven plugin to pick up data from multiple files

I've attached a patch file to implement this.

With this patch, the way to pass in files is now like this:

<src>
<param>src/test/resources/static-data.xml</param>
<param>src/test/resources/sample-data.xml</param>
</src>

the suggested patch is not backward compatible. You cannot change the meaning of "src"

Fixed in rev 10226 and 10227.
New snapshot pushed.