[PATCH v9 0/4] var: -z output, multiple variables, and broken-out idents

This is a reroll of the single patch in v8, split up as Junio asked for, with the changes Phillip asked for on the list.

v8 was one commit doing four things at once. It is now four patches:

  1/4 converts the internal representation of a multi-valued variable
      from a newline-joined string to a string_list, with no change in
      output. Phillip suggested doing this as its own preparatory step.

  2/4 adds "-z", which is what forces the switch to parse_options(), so
      that conversion lives here rather than in 1/4.

  3/4 teaches "git var" to take more than one variable.

  4/4 adds GIT_AUTHOR_NAME and friends.

Changes since v8:

 * GIT_SIGNING_KEY is dropped. Phillip asked three times how it was
   meant to be used, and once I looked properly the answer was that the
   value cannot be interpreted without also reading gpg.format, and that
   in the default configuration it is a committer ident rather than a
   key at all. I would rather leave it out than define a variable I
   cannot describe. Details are in my reply to him on this thread.

 * Asking for several variables no longer exits non-zero just because
   one of them has no value; such a variable is left out of the output
   and the rest are still shown. A non-zero status is now reserved for
   real errors, such as naming a variable that does not exist, so
   callers can detect those from the exit code. A single variable still
   exits 1 when it has no value, as before. This is Phillip's
   GIT_CONFIG_NOSYSTEM point.

 * GIT_CONFIG_GLOBAL is documented as a variable that can have more than
   one value.

 * The commit messages are prose rather than a list of bullet points,
   and no longer narrate how the patch was developed.

The tests use nul_to_q rather than running test_cmp over files containing NUL bytes, which Phillip pointed out in v6. Each patch builds and passes t0007 on its own.

One thing I did not do, and would like an opinion on: for a multi-valued variable in multi-variable mode, rather than emitting a trailing delimiter, each value is shown as its own "VARIABLE=value" entry, which matches "git var -l". Phillip suggested the trailing delimiter and I am happy to switch.

Andrew Pleeter (4):
  var: represent multi-valued variables with a string_list
  var: add "-z" output mode
  var: accept more than one variable
  var: add broken-out identity variables

 Documentation/git-var.adoc |  68 +++++++++--
 builtin/var.c              | 242 +++++++++++++++++++++++++++++--------
 t/t0007-git-var.sh         | 153 +++++++++++++++++++++++
 3 files changed, 403 insertions(+), 60 deletions(-)