A ".dd2 <address>" item would get linked to an internal label, but
references to external addresses weren't doing the appropriate
search through the platform/project symbol list.
This change altered the output of the 2019-local-variables test.
The previous behavior was restored by disabling "nearby" symbol
matching in the project properties.
Updated the "lookup symbol by address" function to ignore local
variables.
Also, minor updates to Applesoft and F8-ROM symbol tables.
After thrashing around a bit, I had to choose between making the
uniquifier more complicated, or making de-duplication a separate
step. Since I don't really expect duplicates to be a thing, I went
with the latter.
Updated the regression test.
This hits most of the edge cases, but doesn't exercise the two
duplicate name situations (var name same as user label, var name
same as project/platform symbol).
Also, fixed a bug in the EditDefSymbol uniqueness check where it
was comparing a symbol to itself.
