[Rd] apply(x, 2, mean) fails if x is a data frame containing a matrix (PR#10902)

[timh at insightful.com]

> data <- data.frame(a=1:5, b=I(matrix(6:15,5)))
> apply(data, 2, mean)
Error in dim(newX) <- c(prod(d.call), d2) : 
  dims [product 10] do not match the length of object [15]


--please do not edit the information below--

Version:
 platform = i386-pc-mingw32
 arch = i386
 os = mingw32
 system = i386, mingw32
 status = 
 major = 2
 minor = 6.2
 year = 2008
 month = 02
 day = 08
 svn rev = 44383
 language = R
 version.string = R version 2.6.2 (2008-02-08)

Windows XP (build 2600) Service Pack 2

Locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

Search Path:
 .GlobalEnv, package:stats, package:graphics, package:grDevices, package:utils, package:datasets, package:methods, Autoloads, package:base