For nonzero values we were leaving Z=prev, which is wrong when Z=0
because the AND result might be zero. Now if Z=1 we leave it alone,
but if Z=0 we now set it to Z=?.
Test 1003-flags-and-branches was testing for the (incorrect)
behavior, so we're now running into a BRK. This is fine.
The label localizer is now always on. The regression tests turned
it off by default, but that's no longer allowed, so the generated
output has changed for many of them. The tests themselves were not
altered.
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.
