action.c: ElementList() reloads from disk
Loads footprints from disk instead of memory. This happens within ElementList
in the following situations:
* An element with the requested refdes is not present.
* The element found by refdes has a different "Desc" field than the requested
<footprint> value.
* The "ForceUpdate" argument is given.
ElementList() is mostly used in the Import() machinery normally through the
gnetlist backend "pcbfwd". Its usage, then, is related to schematic->pcb
annotation and updating. The ability to load updated footprints from disk
avoids the need to restart PCB to use the new versions.