Merge branch 'rs/xdiff-hunk-with-func-line' into maint

Merge branch 'rs/xdiff-hunk-with-func-line' into maint

"git show -W" (extend hunks to cover the entire function, delimited
by lines that match the "funcname" pattern) used to show the entire
file when a change added an entire function at the end of the file,
which has been fixed.

* rs/xdiff-hunk-with-func-line:
  xdiff: fix merging of appended hunk with -W
  grep: -W: don't extend context to trailing empty lines
  t7810: add test for grep -W and trailing empty context lines
  xdiff: don't trim common tail with -W
  xdiff: -W: don't include common trailing empty lines in context
  xdiff: ignore empty lines before added functions with -W
  xdiff: handle appended chunks better with -W
  xdiff: factor out match_func_rec()
  t4051: rewrite, add more tests