Use mkotemp() instead of mkstemp()
Use mkotemp() instead of mkstemp()

This uses mkostemp() instead of mkstemp(), passing along the `O_CLOEXEC` flag,
which makes sure that the file descriptor is closed and won't be leaked into
any child process, which was previously an issue due to a missing fclose()
(#136).

Yubico/yubico-pam,eworm-de/yubico-pam,eworm-de/yubico-pam,Yubico/yubico-pam,eworm-de/yubico-pam,Yubico/yubico-pam