[R] change in behavior of c.trellis

[Richard M. Heiberger]

> library(latticeExtra)
Loading required package: lattice
Loading required package: RColorBrewer
> t11 <- xyplot(1 ~ 1)
> t11
> c(t11, t11)
Warning message:
In formals(fun) : argument is not a function
> version
               _
platform       x86_64-w64-mingw32
arch           x86_64
os             mingw32
system         x86_64, mingw32
status         Patched
major          3
minor          4.3
year           2017
month          12
day            12
svn rev        73903
language       R
version.string R version 3.4.3 Patched (2017-12-12 r73903)
nickname       Kite-Eating Tree
>


the c.trellis seems to work correctly except for the new warning.

There was no warning in 3.3.3.
I first noticed it in 3.4.1

the c.trellis function itself is not changed between 3.3.3 and 3.4.3 Patched.