Merge branch 'maint'

* maint:
  Update draft release notes for 1.6.0.1
  Add hints to revert documentation about other ways to undo changes
  Install templates with the user and group of the installing personality
  "git-merge": allow fast-forwarding in a stat-dirty tree
  completion: find out supported merge strategies correctly
  decorate: allow const objects to be decorated
  for-each-ref: cope with tags with incomplete lines
  diff --check: do not get confused by new blank lines in the middle
  remote.c: remove useless if-before-free test
  mailinfo: avoid violating strbuf assertion
  git format-patch: avoid underrun when format.headers is empty or all NLs

diff --cc diff.c
index 10d54405d21888d41a1e20f27358e15ba5b679d5,f70e6b4912911bd3f3a1d385fce7119a4a8107f6..5923fe281b6ab421f785a1d47afd6dee5711e52d
--- 1/diff.c
--- 2/diff.c
+++ b/diff.c
@@@ -1628,9 -1627,11 +1628,10 @@@ static void builtin_checkdiff(const cha
                xdemitcb_t ecb;
  
                memset(&xecfg, 0, sizeof(xecfg));
+               xecfg.ctxlen = 1; /* at least one context line */
                xpp.flags = XDF_NEED_MINIMAL;
 -              ecb.outf = xdiff_outf;
 -              ecb.priv = &data;
 -              xdi_diff(&mf1, &mf2, &xpp, &xecfg, &ecb);
 +              xdi_diff_outf(&mf1, &mf2, checkdiff_consume, &data,
 +                            &xpp, &xecfg, &ecb);
  
                if ((data.ws_rule & WS_TRAILING_SPACE) &&
                    data.trailing_blanks_start) {