internet.R test hangs if http proxy needed (PR#3108)

Prof Brian Ripley wrote:

We need help, as to reproduce this needs some particular local setup and 
there have been no reports from anyone during the beta-test period for 
1.7.0, nor from previous versions.  (That makes me suspect it is rare 
local setup.)  Can you please debug this further.

It appears to be partly a bug in my impatience:

system.time(httpget("http://www.stats.ox.ac.uk/pub/datasets/csb/ch11b.dat"))
Error in make.socket(host, port = port) : Socket not established
Timing stopped at: 0 0 189 0 0

  The function times out after 189 seconds, whereas my impatience
timeout is 3 minutes. I will upgrade my impatience to the latest version
so that it is compatible with everyone elses.

  At first I thought it was taking 3 * options()$timeout to produce the
timeout in make.socket. A quick investigation shows that to be purely 
coincidental with the initial value of options()$timeout:

options(timeout=2)

system.time(httpget("http://www.stats.ox.ac.uk/pub/datasets/csb/ch11b.dat"))
making socket
Error in make.socket(host, port = port) : Socket not established
Timing stopped at: 0 0 189.04 0 0

  The 189 second timeout appears to be part of our particular local
setup (port 80 is blocked off-site).

options()$timeout seems to have no effect on connections that fail due
to  non-use of our proxies. Is this a bug? The doc claims:

timeout: integer.  The timeout for Internet operations, in seconds.
           Default 60 seconds.

which is a bit vague. If I do something like:
  read.table("http://www.stats.ox.ac.uk/pub/datasets/csb/ch11b.dat")
without setting my proxy I get 189 seconds, regardless of
options()$timeout yet it is undoubtedly an internet operation.

  Back to the original problem: the httpget function in tests/internet.R 
can be modified to obey an http_proxy setting with a fairly simple 
adjustment near the start:

   hp <- Sys.getenv("http_proxy")
   if(hp != ""){
## we need to extract host and port from the proxy:
## split on / or : thusly:
## [http]:[]/[]/[hostname]:[port]
##   1     2  3      4        5
     hpbits <- strsplit(hp,"[/:]")[[1]]
     host <- hpbits[4]
     port <- hpbits[5]
## ask the proxy for the full URL with all its http:// glory:
     rurl <- url
   }else{
## no proxy, connect direct and ask for the URL relative to root:
     host <- urlel[3]
     rurl <- paste(c("", urlel[-(1:3)]), collapse = "/")
   }

  I still have some qualms about tests that rely on things external to 
the test site, but without including a socket server program (which 
would need its own set of tests, I suppose) I cant see any way of 
testing socket functionality without dribbling on the internet at large.