a common part being defined as have a common value.
This is true for most designs but will produce an
incorrect output if two or more parts with the same
value have different footprints, tolerances, voltage
rating, etc.  Also usefull if the following fields
are edited: 
	FIELD1 - manufacture
	FIELD2 - manufacture part number
	FIELD3 - distributor part number
Check in code for now, doc later.