Compile with MSVS 2013 and fix compile error

I had troble trouble when compiling with MSVS 2013,
it says

main.c(103) : error C2065: 'F_OK' : undeclared identifier
main.c(110) : error C2065: 'F_OK' : undeclared identifier
main.c(112) : error C2065: 'F_OK' : undeclared identifier

So I made two patches.

To compile, just do

nmake -f Makefile.msc