For some reason ob-R refuses to compile when it requires ob-comint.
When (require 'ob-comint) is not included in ob-R.el everything
compiles without error, but warnings are thrown because the
arguments to a macro defined in ob-comint are mis-interpreted as
functions.
When (require 'ob-comint) is added to ob-R.el then it throws errors
complaining that the last argument to a function is nil and should
be a string. I don't understand this error at all and can't fix it.
