* Convert Eeschema from manually linked list to DLIST for storing
SCH_ITEM objects.
* Add helper functions to SCH_SCREEN for appending list of SCH_ITEM
objects.
* Fix bug in wire editing code for accurate undo/redo behavior.
* Add member to DLIST to append another DLIST.
* Other minor code cleaning.
* All header files used to create the PCB common library now compile as
stand alone code. This prevents the need to define them in a specific
order to make source code compile properly. It should also now be
possible to relocate the source code to build the common PCB library
to a separate folder.
Maciej Suminski
Wayne Stambaugh
Dick Hollenbeck
dickelbeck