GNU build: Require Boost 1.48

1.48 is needed for Boost.Container, now used by the Core.
On Ubuntu (for example), Boost 1.48 is available since 12.04LTS.

git-svn-id: https://valelab.ucsf.edu/svn/micromanager2/trunk@14417 d0ab736e-dc22-4aeb-8dc9-08def0aa14fd