The cc65 assembler runs in a single pass, which means forward
address references default to 16 bits. For zero-page references
we have to add an explicit width disambiguator. (This is an
unusual situation that only occurs if you have a zero-page .ORG
in the file after code that references it.)
With this change, 2014-label-dp passes, and no other regression
tests were affected.
(issue #40)