ls-remote: introduce --branches and deprecate --heads

We call the tips of branches "heads", but this command calls the
option to show only branches "--heads", which confuses the branches
themselves and the tips of branches.

Straighten the terminology by introducing "--branches" option that
limits the output to branches, and deprecate "--heads" option used
that way.

We do not plan to remove "--heads" or "-h" yet; we may want to do so
at Git 3.0, in which case, we may need to start advertising upcoming
removal with an extra warning when they are used.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-ls-remote.txt

@@ -9,7 +9,7 @@ git-ls-remote - List references in a remote repository
 SYNOPSIS
 --------
 [verse]
-'git ls-remote' [--heads] [--tags] [--refs] [--upload-pack=<exec>]
+'git ls-remote' [--branches] [--tags] [--refs] [--upload-pack=<exec>]
 	      [-q | --quiet] [--exit-code] [--get-url] [--sort=<key>]
 	      [--symref] [<repository> [<patterns>...]]
 
@@ -21,14 +21,16 @@ commit IDs.
 
 OPTIONS
 -------
--h::
---heads::
+-b::
+--branches::
 -t::
 --tags::
-	Limit to only refs/heads and refs/tags, respectively.
+	Limit to only local branches and local tags, respectively.
 	These options are _not_ mutually exclusive; when given
 	both, references stored in refs/heads and refs/tags are
-	displayed.  Note that `git ls-remote -h` used without
+	displayed.  Note that `--heads` and `-h` are deprecated
+	synonyms for `--branches` and `-b` and may be removed in
+	the future.  Also note that `git ls-remote -h` used without
 	anything else on the command line gives help, consistent
 	with other git subcommands.