Bug 122854 There is redundant columns in "available columns" list in "export data" dialog.
Description: There is redundant columns in "available columns" list in "export data" dialog. Steps to reproduce: 1. Preview attached design in web viewer. 2. Select the table and click on "export" button. 3. There is a "detail" column name in "available columns" list which is not data set column.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
* the execution context
		 */
		protected ExecutionContext context;
		/**
		 * create report query definitions for this report.
		 * 
		 * @param report
		 *            entry point to the report
		 * @param context
		 *            the execution context
		 */
		public void buildQuery( Report report, ExecutionContext context )
		{
			this.report = report;
			this.context = context;
			queries = report.getQueries( );
			
			
			queries.clear( );
			queryIDs = report.getQueryIDs( );
			queryIDs.clear( );
			
			for ( int i = 0; i < report.getContentCount( ); i++ )
				report.getContent( i ).accept( this, null );
		}
		/**
		 * Handles query creation and initialization with report-item related
		 * expressions
		 * 
		 * @param item