[Rd] "plot.ts" doesn't respect the value of "pch" (+ blocked from Bugzilla signups)

[Gregory Werbin]

I did a search on Bugzilla for "plot.ts" and didn't find anything on 
this issue. I tried to sign up for Bugzilla to report it, but my e-mail 
address didn't pass your "syntax checking" for a legal e-mail address.

The bug is easily reproducible on my machine as follows:

## start

# generate some data
y <- arima.sim(list(), 150)

# this will definitely dispatch to a ".ts" method
class(y)[1] == 'ts'

# compare and note that `cex = 0.5` has no effect
plot(y, type = 'b', pch = 16)
plot(y, type = 'b', pch = 16, cex = 0.5)

# it works if `y` is coerced back to a regular vector
plot(as.numeric(y), type = 'b', pch = 16, cex = 0.5)

# another way to see the issue
plot.ts(y, type = 'b', pch = 16, cex = 0.5)
plot.default(y, type = 'b', pch = 16, cex = 0.5)

## end

Skimming through source code for `plot.ts`, it seems like the `cex` 
argument is being "eaten" by a `...` somewhere without being properly 
passed to `plot.default`.

The output of `R.version` is:
platform       x86_64-apple-darwin15.5.0
arch           x86_64
os             darwin15.5.0
system         x86_64, darwin15.5.0
status
major          3
minor          3.1
year           2016
month          06
day            21
svn rev        70800
language       R
version.string R version 3.3.1 (2016-06-21)
nickname       Bug in Your Hair

Greg