Modified the behavior of SelectCopy() so that it surveys cell

instance names in both the selection and in the root edit CellDef,
and then wipes duplicate names from the selection and regenerates
unique IDs.  This avoids the unexpected behavior displayed by
magic in which a "copy" function renames the *original* instance
and gives the original name to the copied instance.  This is not
only unexpected, but causes an error in which "undo" after
multiple copies fails to remove earlier copies because the name
change was not recorded, and the instance can no longer be found
by name.

database/database.h.in

@@ -983,6 +983,7 @@ extern int  DBScaleCell();
 extern TileType DBTechNameTypes();
 extern void DBTreeFindUse();
 extern void DBGenerateUniqueIds();
+extern void DBSelectionUniqueIds();
 extern TileType DBInvTransformDiagonal();
 extern bool DBIsSubcircuit();
 extern int  DBSrPaintNMArea();