Value type of param_trait<cl_event_info, CL_EVENT_COMMAND_EXECUTION_STATUS>::param_type is cl_uint. Since the value can by negative for errors, it should be signed as is written in the documentation.
Thus checking for errors is more complicated (e.g.):
cl_uint status = event.getInfo<CL_EVENT_COMMAND_EXECUTION_STATUS>();
if(status > 0x7FFFFFF)
// error command execution
Thanks for the report. I've fixed it in the internal version of cl.hpp, and it will appear whenever the next version is released.