Merge branch 'ps/fetch-output-format'

"git fetch" learned the "--porcelain" option that emits what it did
in a machine-parseable format.

* ps/fetch-output-format:
  fetch: introduce machine-parseable "porcelain" output format
  fetch: move option related variables into main function
  fetch: lift up parsing of "fetch.output" config variable
  fetch: introduce `display_format` enum
  fetch: refactor calculation of the display table width
  fetch: print left-hand side when fetching HEAD:foo
  fetch: add a test to exercise invalid output formats
  fetch: split out tests for output format
  fetch: fix `--no-recurse-submodules` with multi-remote fetches

Author: gitster

Documentation/fetch-options.txt

@@ -78,6 +78,13 @@ linkgit:git-config[1].
 --dry-run::
 	Show what would be done, without making any changes.
 
+--porcelain::
+	Print the output to standard output in an easy-to-parse format for
+	scripts. See section OUTPUT in linkgit:git-fetch[1] for details.
++
+This is incompatible with `--recurse-submodules=[yes|on-demand]` and takes
+precedence over the `fetch.output` config option.
+
 ifndef::git-pull[]
 --[no-]write-fetch-head::
 	Write the list of remote refs fetched in the `FETCH_HEAD`

Documentation/git-fetch.txt

@@ -204,6 +204,15 @@ representing the status of a single ref. Each line is of the form:
  <flag> <summary> <from> -> <to> [<reason>]
 -------------------------------
 
+When using `--porcelain`, the output format is intended to be
+machine-parseable. In contrast to the human-readable output formats it
+thus prints to standard output instead of standard error. Each line is
+of the form:
+
+-------------------------------
+<flag> <old-object-id> <new-object-id> <local-reference>
+-------------------------------
+
 The status of up-to-date refs is shown only if the --verbose option is
 used.