The code was making an unwarranted assumption about how the flags
were being set. For example, ORA #$00 can't know if the previous
contents of the accumulator were nonzero, only that the instruction
hasn't made them nonzero, but instead of marking the Z-flag
"indeterminate" it was leaving the flag in its previous state. This
produces incorrect results if the previous instruction didn't set
its flags from the accumulator contents, e.g. it was an LDX.
Test 1003-flags-and-branches has been updated to test these states.
If you set things up just right, it's possible for flag status
changes to fail to get merged.
Added a regression test to 1003-flags-and-branches.
Also, tweaked the instruction operand editor to be a bit smoother
from the keyboard: added alt-key shortcuts, and put the focus on the
OK button after creating/editing a label so you can just hit the
return key twice.
There are some useful interactions between C/N and maybe Z. Added
a quick test to 1003-flags-and-branches.
Also, updated the 2008-address-changes tests. Change b37d3dba
extended the nearby-target range of out-of-file symbols by one, so
one line that didn't get an operand label now does.
