Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/DataEngineSession.java
{
			this.scope = new ImporterTopLevel( cx );
		}
		new CoreJavaScriptInitializer( ).initialize( cx, scope );
		Context.exit( );
		
	}
	
	/**
	 * Get a context property according to given key.
	 * 
	 * @param key
	 * @return
	 */
	public Object get( String key )
	{
		if( key!= null )
			return this.context.get( key );
		return null;
	}
	
	/**
	 * Set a context property with given key.
	 * 
	 * @param key
	 * @param value
	 */
	public void set( String key, Object value )
	{
		this.context.put( key, value );