Use autoconf
Merge pull request #45 from cookpad/use_autoconf

use autoconf in nutcracker.spec
Add #include for nc_event.h to nc_stats.c so that we have the function prototype for evbase_create.
Provide support for platforms without backtrace support (e.g. FreeBSD).
Produce an error message when ./configure is run if neither epoll or kqueue is supported, instead of producing confusing link errors because both nc_epoll.c and nc_kqueue.c are empty.
Fix typo in configure.ac, remove cast to void * in EV_SET invocations.
Merge remote-tracking branch 'upstream/master' into kqueue_pull