Bug 6672 jar no longer exported after attach source
1206 1. Create a project test. 2. Add a jar (say resources.jar) to the classpath and export the entry 3. Attach source (say resourcessrc.zip) to the jar. Notice, the jar is no longer exported - this information is discarded during the attach source process.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
* Gets the source attachment root chosen by the user
	 */
	public IPath getSourceAttachmentRootPath() {
		if (getSourceAttachmentPath() == null) {
			return null;
		} else {
			return new Path(fPrefixField.getText());
		}
	}
		
	/**
	 * Creates the control
	 */
	public Control createControl(Composite parent) {
		fSWTWidget= parent;
		
		Composite composite= new Composite(parent, SWT.NONE);	
		
		MGridLayout layout= new MGridLayout();
		layout.marginHeight= 0;
		layout.marginWidth= 0;
		layout.minimumWidth= SWTUtil.convertWidthInCharsToPixels(80, composite);
		layout.numColumns= 4;		
		composite.setLayout(layout);
		
		int widthHint= SWTUtil.convertWidthInCharsToPixels(fIsVariableEntry ? 50 : 60, composite);
		
		
		MGridData gd= new MGridData(MGridData.HORIZONTAL_ALIGN_FILL);
		gd.horizontalSpan= 4;