This makes screen:snapshot_util() generate code with the new
screen:add_extra_attr_ids { ... } pattern. For convenience,
the old-style configuration is still detected and supported (until
all tests have been refactored, which is my goal for the 0.11 cycle)
Remove the last traces of the "ignore" attr anti-pattern. This code
is no longer functional, it is just "ignore" argument being passed around
like a hot potato at this point.
a4b5549655