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.
If PTR is defined as an external symbol, we were automatically
symbol-ifying PTR+1. Now we also symbolify PTR+2. This helps with
24-bit pointers on the 65816, and 16-bit "jump vectors", where the
address is preceded by a JMP opcode.
Removed the "AMPERV_" symbol I added to make the tutorial look
right.