remove use of boost::thread/boost::mutex; bump glibmm requirement to 2.30 in order...

remove use of boost::thread/boost::mutex; bump glibmm requirement to 2.30 in order to pick up Glib::Threads::Mutex which can be used statically, use that to replace boost::mutex; add required inclusion of <cerrno> in a couple of places

git-svn-id: svn://localhost/ardour2/branches/3.0@13076 d708f5d6-7413-0410-9779-e7cbd77b26cf