MFC r249811:
Literally follow POSIX:
If the bs= expr operand is specified and no conversions other than sync,
noerror, or notrunc are requested, the data returned from each input
block shall be written as a separate output block.

PR:	standards/177742


git-svn-id: svn://svn.freebsd.org/base/stable/9@250328 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Merge remote-tracking branch 'upstream/svn_stable_9' into svn_stable_9