split --filter=CMD: last call

[Jim Meyering]

I've fixed the problems spotted by Pádraig Brady in the first round,
  http://thread.gmane.org/gmane.comp.gnu.coreutils.general/1138
and have merged all code-changing commits into Karl's initial one.
This is rebased against the current head, and does compile ;-)
and passes all tests.

[PATCH 1/3] split: accept new output --filter=CMD option
[PATCH 2/3] tests: test split's new --filter=CMD option
[PATCH 3/3] doc: document split's new --filter=CMD option

 NEWS               |   10 ++
 doc/coreutils.texi |   23 ++++-
 src/split.c        |  227 +++++++++++++++++++++++++++++++++++++++++++++++------
 tests/Makefile.am  |    1 
 tests/split/filter |   45 ++++++++++
 5 files changed, 281 insertions(+), 25 deletions(-)

Feedback welcome,

Jim

P.S. This new test, "tests/split/filter" is in a new,
otherwise-empty directory.
There were enough tests/misc/split* (6) tests that moving them
into their own seems worthwhile.  I'll do that separately.