[Rd] update.formula and backticked colons

[Sundar Dorai-Raj]

I just noticed the following in update.formula and I'm wondering if
this behavior is the intention of the developers. Here's an example:

update(`a: b` ~ x, ~ . + y)

Note now that the response has no backticks and is interpreted as a:b
(i.e. ":" is now an operator). This is because in update.formula the
call to terms.formula uses simplify = TRUE. I'm working with data that
has a lot of colons in their names and for reporting purposes I don't
want to use make.names to avoid this situation. I do have a solution
which simply avoids using update.formula, but I wonder if the
developers would consider removing the "simplify" argument and allow
it to be passed through "...", which is currently ignored by
update.formula. Alternatively, add a simplify=TRUE to the
update.formula call, which can manually be set to FALSE by the user.

I would love to hear any comments or criticisms of my findings.

Thanks,

--sundar