Sadly, each unit of a component can have its own unique fields. This
change finds the last non blank field and records it. Last guy wins
and the order of units occuring in a schematic hierarchy is variable.
Therefore user is best off setting fields into only one unit. But this
scavenger algorithm will find any non blank fields in all units and use
the last non-blank field for each unique field name.
Fixes lp:1471417
https://bugs.launchpad.net/kicad/+bug/1471417
50716c9015