Fix for older kernels to make sure O_CLOEXEC is defined

This patch fixes an issue where I was getting build errors that O_CLOEXEC was undefined on an older 2.6.32 kernel. Even though the flag is supported in this kernel it was not getting defined.
Merge pull request #246 from andrewfenn/patch-1

Fix for older kernels to make sure O_CLOEXEC is defined