Fix warnings when compiling with VS2013 Nov CTP

These two lines caused a C4800 warning when compiling with the Nov 2013
Visual Studio CTP.
(selene\primitives.h(58): warning C4800: 'int' : forcing value to bool
'true' or 'false' (performance warning))
Merge pull request #29 from PeterTh/master

Fix warnings when compiling with VS2013 Nov CTP