updates.laptop.org updated for new build naming

[Daniel Drake]

Hi,

I updated the code for updates.laptop.org to be ready for the new
filename scheme of 12.1.0 and onwards:
http://wiki.laptop.org/go/Release_Process#Build_filenames

This is the server used by olpc-update.

I am pretty sure I kept compatibility with all stable releases, and
all post-2010 development streams.
If anything is broken (i.e. you can't olpc-update to a given version),
please shout.

olpc-update for 12.1.0 will be enabled soon, just one small bug to fix first.

Thanks,
Daniel