Guard post-processing vim scripts

These would edit the file while making a vim macro, which (if there
wasn't anything that needed editing) could result in stuff
deleted/changed unnecessarily at the start of the file.
Disable https for asciicasts

For some reason the https players were having trouble getting the right
size for the asciicast.

See
https://github.com/sickill/asciinema.org/issues/126#issuecomment-32045430
for more info.