Merge branch 'sp/clip-read-write-to-8mb'

Send a large request to read(2)/write(2) as a smaller but still reasonably large chunks, which would improve the latency when the operation needs to be killed and incidentally works around broken 64-bit systems that cannot take a 2GB write or read in one go. * sp/clip-read-write-to-8mb: Revert "compat/clipped-write.c: large write(2) fails on Mac OS X/XNU" xread, xwrite: limit size of IO to 8MB