boost: bump to version 1.52.0

Can someone review the patch to bump boost version before releasing next buildroot RC?

The patch is available in buildroot's patchwork at
http://patchwork.ozlabs.org/patch/197508/

To bump boost, I needed to add dependance on BR2_LARGEFILE and exclude the new context lib, because this last fails during compilation : an include is missing and uintptr_t is not found. I will open a ticket on boost's bug tracker.