Shush the backtrace_locations, too

[amomchilov]

Fixes #739

Didn't change any tests, because I couldn't find any tests that covered this behaviour.

[amomchilov]

How do we feel about giving $! a more reasonable name?

Suggested change

	if $!
	lib = File.expand_path("..", __FILE__)
	$!.backtrace.reject! { |line| line.start_with?(lib) } unless $!.backtrace.frozen?
	unless $!.backtrace.frozen?
	$!.backtrace.reject! { |line| line.start_with?(lib) }
	$!.backtrace_locations.reject! { |line| line.path.start_with?(lib) }
	end
	end
	error = $!
	if error
	lib = File.expand_path("..", __FILE__)
	unless error.backtrace.frozen?
	error.backtrace.reject! { |line| line.start_with?(lib) }
	error.backtrace_locations.reject! { |line| line.path.start_with?(lib) }
	end
	end

[amomchilov]

Found this confusing. Is there any reason to use ensure + $!, rather than just rescue => e + raise e?

I thought perhaps because a re-raise would introduce a new frame into the backtrace, but it doesn't

demo

#!/opt/rubies/3.4.2/bin/ruby

begin
 raise
rescue => e
  raise e
end

# Prints:
# demo.rb:4:in '<main>': unhandled exception

# As you see, line 5 and 6 aren't in the backtrace.