advapi32: Fall back to /dev/random if /dev/urandom can't be opened, and add warnings if opening either fails

[Juan Lang]

Hi Austin,

> FWIW: http://en.wikipedia.org/wiki/Urandom
(snip)
> "A software program called EGD (entropy gathering daemon) is a common
> alternative for Unix systems which do not support the /dev/random
> device.

Yep, I know.  The problem with using EGD is that there isn't a
standard path to it.  Because /dev/urandom is so commonly available,
adding a configuration option and code for such a rarely used feature
didn't seem worth it.

Thanks,
--juan