Update Doxyfile for Doxygen v1.8.6

This shouldn't have changed anything of substance.
Fix warning under gcc 4.8

Close #46 "Building fails under GCC 4.8" as it compiles cleanly for me
under gcc 4.8.2.
Fix 100% CPU and wedges with gcc 4.8

This was caused by http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58931
In short, waiting for a monotonic clock's infinity would overflow,
causing no wait at all. Worse yet, the mutex wouldn't even be released
and reacquired, so all other threads get starved.

The work-around in this commit is to sleep for no longer than one hour
(after an hour, you'll get a spurious interrupt).

Fix #49: 100% cpu in event loop
Fix #50: leader process hangs after Conrol-C
Replace remaining uses of std::condition_variable with Core::ConditionVariable

These weren't causing any immediate known problems, but it seems wise to
avoid using std::condition_variable directly in light of the previous
commit.