Fix sending interrupt commands after SIGINT

Related to #182. I'm not really sure this is the best solution, but it works at least.

I was experimenting with the code and it appears that for some reason the `catch Vim:Interrupt` statement was never executing. I couldn't trace down why. This is sorta an ugly hack now, but I am not sure what else to try catching if Vim:Interrupt isn't working.

It also appeared from my debugging that the `options` never had the session in it, but `self` did, so I changed the code to copy the session id from `self`. Again, not sure whether `options` *should* have it, or if this is okay/correct. Pretty new to Vimscript, so just tracing method calls is a challenge :smile:.