NFS and auto-update fixes

Hi Stephan

I've created a couple of patches for two different, but related, issues.

1. Regex/timestamp issues when updating BCM2385 binaries  - see issue #1691 for details. These are minor problems, but the fix is trivial.

2. Fix auto-update to work with NFS Boot (issue #1653) - this is a fairly straight forward solution, it just detects if nfs is being used for netboot and adjusts the targets accordingly. However, since the SD card isn't actually mounted, a small hack is needed to in order to mount the SD card as `/bootroot`, and this assumes `/dev/mmcbl0p1`. Not sure if other devices are using NFS to boot, in which case a similar mount point may be required for them too, and for now this solution only works for the Pi.

Both patches have been tested with build r12806 on Raspberry Pi.

Regards
Milhouse