Blocknotify calls now use the C++11 threading API instead of Boost
Blocknotify calls now use the C++11 threading API instead of Boost

The Boost variant seems to be causing issues and sometimes does not fire
the blocknotify calls. With some luck, this might resolve it.

neutroncoin/neutron,neutroncoin/neutron,neutroncoin/neutron,neutroncoin/neutron