Bug 119340 [PopupDialog] - need constant for horizontal spacing
PopupDialog provides a constant for vertical spacing used in the contents, but not for horizontal spacing.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/PopupDialog.java
layout.verticalSpacing = POPUP_VERTICALSPACING;
		composite.setLayout(layout);
		GridData gd = new GridData(GridData.FILL_BOTH);
		composite.setLayoutData(gd);
		
		if (hasTitleArea()) {
			createTitleMenuArea(composite);
			titleSeparator = createHorizontalSeparator(composite);
		}
		
		dialogArea = createDialogArea(composite);
		
		if (hasInfoArea()) {
			infoSeparator = createHorizontalSeparator(composite);
			createInfoTextArea(composite);
		}
		applyColors(composite);
		applyFonts(composite);
		return composite;
	}
	/**
	 * Creates and returns the contents of the dialog (the area below the title
	 * area and above the info text area.
	 * <p>
	 * The <code>PopupDialog</code> implementation of this framework method
	 * creates and returns a new <code>Composite</code> with standard margins
	 * and spacing.
	 * <p>
	 * The returned control's layout data must be an instance of
	 * <code>GridData</code>. This method must not modify the parent's