[Rd] r cmd build

[Gabor Grothendieck]

On Windows Vista hhc.exe is not available.  One can do this on an
install:

rcmd install --docs=normal myPackage

to avoid the message about hhc.exe; however,
"rcmd build" does not appear to support --docs=normal so one cannot
do a build without getting a message about hhc.exe (although the build
still proceeds).