CuckooFilter uses tmpnam()

[jsteemann]

g++5.4 complains:

CMakeFiles/PerformanceTest.dir/tests/PerformanceTest.cpp.o: In function `CuckooFilter<Key, HashWithSeed<Key, 16045690984833335023ul>, HashWithSeed<Key, 12379814471884804660ul>, HashWithSeed<unsigned short, 18364758984297693985ul>, std::equal_to<Key> >::CuckooFilter(bool, unsigned long)':
/home/steemann/Downloads/CuckooMap/include/cuckoomap/CuckooFilter.h:79: warning: the use of `tmpnam' is dangerous, better use `mkstemp'

Quoting "man 3 tmpnam":

 BUGS
       Never use this function.  Use mkstemp(3) or tmpfile(3) instead.

Should indeed be fixed to generate "better" tempfile names.

[dhly-etc]

We will likely replace tempfiles entirely in order to make the structure persistent, instead providing a directory to CuckooMap which can then provide filenames to the InternalCuckooMap and CuckooFilter instances. The use of tmpfile now is just a quick-and-dirty way to allow memory-mapped files without changing the interface, and will certainly need a fix in the future.