Bug 205049 Other plug-ins should be able to define default content generator
Currently only the content generator can define which plug-ins it can be the default for - we need a way for plug-ins to refer back to the marker support for thier own generator.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/provisional/views/markers/MarkerComparator.java
value = fields[i].compare(item0, item1);
			if (value == 0)
				continue;
			return value;
		}
		return 0;
	}
	/**
	 * Switch the priority of the field from ascending to descending or vice
	 * versa.
	 * 
	 * @param field
	 */
	public void reversePriority(MarkerField field) {
		if (descendingFields.remove(field))
			return;
		descendingFields.add(field);
	}
	/**
	 * Set field to be the first sort field.
	 * 
	 * @param field
	 */
	void setPrimarySortField(MarkerField field) {
		if (fields[0] == field) {
			reversePriority(field);
			return;
		}
		int insertionIndex = 1;
		MarkerField[] newFields = new MarkerField[fields.length];