Fixed the Boost library search

The cmake supplied FindBoost.cmake is broken (at least in cmake 2.8) and
the system libraries are always returned even when BOOST_ROOT is specifically
set and system search paths disabled. This commit provide a work-around for
this problem where the BOOST_ROOT path (if set) is searched for boost libs.
cmake: fixed hdf5 dependency to use find_package
cmake: removed the direct dependency on zlib

This dependency is driven by HDF5 - and FindHDF5 actually adds -lz to the
linker flags by itself.