respect use_short_path on trace

[ko1]

fix #701

[ko1]

memo

# rdbg -n target.rb

binding.eval(<<~RUBY, File.expand_path("~/xyzzy.rb"))
def foo
  a = 1
  b = 2
  a + b
end
RUBY

binding.b do: <<~DBG
  trace line
  config set use_short_path true
DBG

foo