Using host Linux (Ubuntu 12.04); performance was abysmal.

On initial load of localhost:4000, the http calls for
additional Javascript files via the browser appears to take
more than a few minutes with *.js endpoints loading in one
file at a time very slowly.

It was observed that the Ruby process was consistently
pegged at 95% and up.  This behaviour is not observed
using a Mac OSX.

However, adding a single core to the guest OS
(from 1 to 2) improved performance considerably.

The patch detects if the host system is Mac OSX or
Linux and attempts to assign the same number of cores
as is present on the host.
Merge pull request #2567 from ffernand/additional_cores_for_guest_os

Using host Linux (Ubuntu 12.04); performance was abysmal.