Added support for "relative" address regions to the Merlin 32 and cc65
code generators. These generate "flat" address directives, and so
were a little more complicated.
Suppressed generation of relative operands for non-addressable regions.
Also, tweaked the 20250-nested-regions test to include a negative
relative region offset.
Implemented "is relative" flag. This only affects source code
generation, replacing ".arstart <addr>" with ".arstart *+<value>".
Only output by 64tass and ACME generators.
Added a bold-text summary to radio buttons in address region edit
dialog. This makes it much easier to see what you're doing. Added
a warning to the label edit dialog when a label is being placed in
a non-addressable region.
Modified double-click behavior for .arstart/.arend to jump to the
other end when the opcode is clicked on. This matches the behavior
of instructions with address operands.
Reordered Actions menu, putting "edit operand" at the top.
Fixed AddressMap entry collision testing.
Fixed PRG issue with multiple address regions at offset +000002.
Added regression tests. Most of the complicated stuff with regions
is tested by unit tests inside AddressMap, but we still need to
exercise nested region code generation.
