Seamless loop rendering and Live-Looping

Came up with two relatively simple to implement features that would improve Renoise:

First is an option to render the selection / column / track / pattern in the second pass, as that would include the FX tail right at the start and create a seamless loop that includes any nice FX you might have put on the channel.

Second is the option to automatically punch out the recording at the end of the pattern. That way, people with e.g. a guitar can record something and then playback would continue looped without recording any further, while they can keep playing live to the recording.