Buffered outputting lacks robustness

While running simulations I got the following problems on some instances:

[host5045:job_86f52a!5427:(1086154) 471775.100000] [task_execution/INFO] Task 'phg 5427'4811'' finished
[master_host:server:(2) 472020.000000] /home/mpoquet/batsim/src/export.cpp:972: [root/CRITICAL] Writing error: buffer has been completely filled, some information might have been lost. Please increase Batsim's output temporary buffers' size
Backtrace (displayed in process server):
---> 'PStateChangeTracer::add_pstate_change(double, MachineRange, int) at /home/mpoquet/batsim/src/export.cpp:970 (discriminator 14), 0x55ab3b590c88'
---> 'server_on_pstate_modification(ServerData*, IPMessage*) at /home/mpoquet/batsim/src/server.cpp:314, 0x55ab3b62c16a'
---> 'std::_Function_handler<void (ServerData*, IPMessage*), void (*)(ServerData*, IPMessage*)>::_M_invoke(std::_Any_data const&, ServerData*&&, IPMessage*&&) at /usr/include/c++/6/functional:1733, 0x55ab3b6341ff'
---> 'std::function<void (ServerData*, IPMessage*)>::operator()(ServerData*, IPMessage*) const at /usr/include/c++/6/functional:2128, 0x55ab3b631ced'
---> 'server_process(int, char**) at /home/mpoquet/batsim/src/server.cpp:105, 0x55ab3b62a719'
---> 'simgrid::xbt::MainFunction<int (*)(int, char**)>::operator()() const at /home/mpoquet/simgrid/include/xbt/functional.hpp:45, 0x7f04e6b46fc9'