QueryEngine.performSelection() loses any custom table properties #42

What steps will reproduce the problem?
1. Implement a DataTableGenerator that adds custom table properties with 
Capabilities.NONE
2. Run any query with a select statement
3. Any custom table properties will be gone in the result table

You would expect that the table properties were preserved.

This is due to the construction of a new DataTable instance without copying 
over any custom properties

http://code.google.com/p/google-visualization-java/source/browse/trunk/src/main/
java/com/google/visualization/datasource/query/engine/QueryEngine.java#317 

The fix would be to ensure that in any methods where the QueryEngine breaks the 
chain, and returns a different DataTable instance than the one passed in, the 
custom table properties are copied over into the new DataTable instance.