Replaced hardcoded boost libs with CMake variables.
Shared boost libraries are now searched for by default.

To search for static boost libs configure with Boost_USE_STATIC_LIBS=ON
from the command line or as a parameter to ccmake.
One more fix for automatic boost build when boost was not found.
Boost_LIBRARIES is also not cached by FindBoost.cmake.
Merge pull request #126 from bilke/BoostFix

Replaced hardcoded boost libs with CMake variables.
This enables linking against shared libraries.