add closefrom() call

[Joerg Sonnenberger]

On Mon, Jul 09, 2007 at 11:46:14PM -0400, Ighighi wrote:
> Calling F_MAXFD everytime we close a file descriptor would be heavy 
> having too much fd's.
> On the other hand, it wouldn't make much a difference to just start from 
> getdtablesize() - 1.

I fully agree. That is the second version of closefrom in DragonFly --
for the purpose of libc_r BTW.

Joerg