libcurl support and curlGetHeaders warning message in R CMD check

Dear R devel,

Is libcurl support required to run R.devel, or is it optional?

I'm compiling R.devel on an older Debian machine  that only has libcurl
version 7.21.0

The R news file says

"
Sun, 25 Jan 2015
CHANGES IN R-devel NEW FEATURES

     Optional use of ?libcurl? (version 7.28.0 from Oct 2012 or later)
for Internet access (including on Windows):

...

CHANGES IN R-devel UTILITIES

     ?R CMD check --as-cran? checks existence and accessibility of URLs
in the ?DESCRIPTION? file and in the help files.
"

Which seems to suggest libcurl support is optional.   The build process
seems to correctly detect that I have an old version of libcurl

checking if libcurl version >= 7.28.0... no

 > capabilities('libcurl')

libcurl
   FALSE

But when I try to build any packages with R.devel (for pre-release
testing) I get lots and lots of Notes/errors like:


Found the following (possibly) invalid URLs:
   URL: http://statnet.org/
     From: DESCRIPTION
     Status: Error
     Message: curlGetHeaders is not supported on this platform

Maybe this url check should first verify that libcurl is available?


If it is the case that libcurl is required for R CMD check --as-cran,
I'll try to follow up with R debian for how to get appropriate version.
(seems like libcurl 7.28 is not yet included in a stable Debian release?)

Thanks for your help,

best,
  -skye