Build System: remove USE_STD_COMPLEX_TREE_LEAFS flags

Bump up ROOT version to 5.34. Remove all appearances of
USE_STD_COMPLEX_TREE_LEAFS flag.
Build System: Bump up CMake version to 3.0

sic!
Build System: Cleanup main build script

sic!
Build System: Warn user if compiler is outdated/unsupported

sic!
Build System: Improve script that compiles BOOST libraries

Add check, whether BOOST_ROOT environment variable is set. Add flag to
bjam that forces rebuild.