Fixed umask for mkstemp
Fixed umask for mkstemp

Now it is securely set to 077 before calling mkstemp. See
strace:

[pid 28806] umask(0)                    = 022
[pid 28806] umask(077)                  = 0
[pid 28806] open("/tmp/fbr_buffer.FjJ3le",O_RDWR|O_CREAT|O_EXCL, 0600) = 6
[pid 28806] umask(022)                  = 077
[pid 28806] unlink("/tmp/fbr_buffer.FjJ3le") = 0

Lupus/libevfibers,Lupus/libevfibers,Lupus/libevfibers