Merge branch 'cn/branch-set-upstream-to'

"git branch --set-upstream origin/master" is a common mistake to
create a local branch 'origin/master' and set it to integrate with
the current branch.  With a plan to deprecate this option, introduce
"git branch (-u|--set-upstream-to) origin/master" that sets the
current branch to integrate with 'origin/master' remote tracking
branch.

* cn/branch-set-upstream-to:
  branch: deprecate --set-upstream and show help if we detect possible mistaken use
  branch: add --unset-upstream option
  branch: introduce --set-upstream-to

diff --cc builtin/branch.c
index 297be4ec4075e7a5877366217d780d6c29b3271b,5e95e3568a33c8d5f1cea02a882cae43892c2e17..e61b0ece2199f0d2b637cd2ce879105280c38d21
--- 1/builtin/branch.c
--- 2/builtin/branch.c
+++ b/builtin/branch.c
@@@ -720,20 -719,22 +721,22 @@@ int cmd_branch(int argc, const char **a
        struct commit_list *with_commit = NULL;
  
        struct option options[] = {
 -              OPT_GROUP("Generic options"),
 +              OPT_GROUP(N_("Generic options")),
                OPT__VERBOSE(&verbose,
 -                      "show hash and subject, give twice for upstream branch"),
 -              OPT__QUIET(&quiet, "suppress informational messages"),
 -              OPT_SET_INT('t', "track",  &track, "set up tracking mode (see git-pull(1))",
 +                      N_("show hash and subject, give twice for upstream branch")),
 +              OPT__QUIET(&quiet, N_("suppress informational messages")),
 +              OPT_SET_INT('t', "track",  &track, N_("set up tracking mode (see git-pull(1))"),
                        BRANCH_TRACK_EXPLICIT),
 -              OPT_SET_INT( 0, "set-upstream",  &track, "change upstream info",
 +              OPT_SET_INT( 0, "set-upstream",  &track, N_("change upstream info"),
                        BRANCH_TRACK_OVERRIDE),
 -              OPT__COLOR(&branch_use_color, "use colored output"),
 -              OPT_SET_INT('r', "remotes",     &kinds, "act on remote-tracking branches",
+               OPT_STRING('u', "set-upstream-to", &new_upstream, "upstream", "change the upstream info"),
+               OPT_BOOLEAN(0, "unset-upstream", &unset_upstream, "Unset the upstream info"),
 +              OPT__COLOR(&branch_use_color, N_("use colored output")),
 +              OPT_SET_INT('r', "remotes",     &kinds, N_("act on remote-tracking branches"),
                        REF_REMOTE_BRANCH),
                {
 -                      OPTION_CALLBACK, 0, "contains", &with_commit, "commit",
 -                      "print only branches that contain the commit",
 +                      OPTION_CALLBACK, 0, "contains", &with_commit, N_("commit"),
 +                      N_("print only branches that contain the commit"),
                        PARSE_OPT_LASTARG_DEFAULT,
                        parse_opt_with_commit, (intptr_t)"HEAD",
                },

diff --cc t/t3200-branch.sh
Simple merge