Last call: removing the INT_MAX limit on max i/o size

This is a notification to allow you to comment on the patch before the
commit.

I will commit the latest version of the patch to remove the limitation
of the maximal i/o size for read/write syscalls to INT_MAX in the
beginning of the next week.

The change is available at
http://people.freebsd.org/~kib/misc/uio_resid.10.patch
various versions of it were discussed with Bruce Evance and David Schultz.

Patch does not enable SSIZE_MAX-sized i/o by default, hiding this under
debug.iosize_max_clamp sysctl. Effectively, the patch becomes the pass
to change various ints into ssize_t.