[Rd] parallel::detectCores() bug on Raspberry Pi B+

[Paul Gilbert]

In R 3.3.2 detectCores() in package parallel reports 2 rather than 1 on 
Raspberry Pi B+ running Raspbian. (This report is just 'for the record'. 
The model is superseded and I think no longer produced.)  The problem 
seems to be caused by

  grep processor /proc/cpuinfo
processor	: 0
model name	: ARMv6-compatible processor rev 7 (v6l)

(On Raspberry Pi 2 and 3 there is no error because the model name lines are

  model name	: ARMv7 Processor rev 5 (v7l)
  model name	: ARMv7 Processor rev 4 (v7l)
)