Changed function to first close standard input (this may
fail but we don't care) and then try to open /dev/null (this
may fail but it shouldn't on Unix platforms plus we don't
know what to do in such case anyways).  Since standard input
has the "zeroth" descriptor number next "open" will use it.

Since there is no "/dev/null" on Windows (It's not even
a valid path!) the second step is skipped if WIN32 is
defined.

As a final touch, since the function consists of merely two
function calls it has been moved to header file and declared
static inline.

[mk: un-inline daemonize_close_stdin()]