little cleanups
added fortuna_source_timer
Revert "don't keep config as const"
Mutexes are non-copyable and non-movable anyway, so it's not a problem to have const members.

This reverts commit 96443434d0168e8c26c38f78a12d9740c494e491.
libfortuna: removed some nonsense from monitor, improved readability
libfortuna::Generator: improve static_assert
fortuna_source_timer: fix int to byte conversion problem
no pass by nonconst ref; monitor: replaced exec by exec_ro and exec_rw, using boost::shared_mutex
libfortuna::Accumulator: replace some one-line lambdas with bind and mem_fn
libfortuna::Accumulator: remove some noexcept
added subdir-objects to AM_INIT_AUTOMAKE