patch 8.1.0037: cannot easily append lines to another buffer

Problem:    Cannot easily append lines to another buffer.
Solution:   Add appendbufline().
diff --git a/src/testdir/test_bufline.vim b/src/testdir/test_bufline.vim
index b886e99..b110c44 100644
--- a/src/testdir/test_bufline.vim
+++ b/src/testdir/test_bufline.vim
@@ -1,4 +1,4 @@
-" Tests for setbufline() and getbufline()
+" Tests for setbufline(), getbufline(), appendbufline()
 
 source shared.vim
 
@@ -65,3 +65,28 @@
   call delete('Xscript')
   call delete('Xtest')
 endfunc
+
+func Test_appendbufline()
+  new
+  let b = bufnr('%')
+  hide
+  call assert_equal(0, appendbufline(b, 0, ['foo', 'bar']))
+  call assert_equal(['foo'], getbufline(b, 1))
+  call assert_equal(['bar'], getbufline(b, 2))
+  call assert_equal(['foo', 'bar'], getbufline(b, 1, 2))
+  exe "bd!" b
+  call assert_equal([], getbufline(b, 1, 2))
+
+  split Xtest
+  call setline(1, ['a', 'b', 'c'])
+  let b = bufnr('%')
+  wincmd w
+  call assert_equal(1, appendbufline(b, 4, ['x']))
+  call assert_equal(1, appendbufline(1234, 1, ['x']))
+  call assert_equal(0, appendbufline(b, 3, ['d', 'e']))
+  call assert_equal(['c'], getbufline(b, 3))
+  call assert_equal(['d'], getbufline(b, 4))
+  call assert_equal(['e'], getbufline(b, 5))
+  call assert_equal([], getbufline(b, 6))
+  exe "bwipe! " . b
+endfunc
diff --git a/src/testdir/test_edit.vim b/src/testdir/test_edit.vim
index 3af8c4c..ab2fe7c 100644
--- a/src/testdir/test_edit.vim
+++ b/src/testdir/test_edit.vim
@@ -527,7 +527,7 @@
   " Tab in completion mode
   let path=expand("%:p:h")
   new
-  call setline(1, [path."/", ''])
+  call setline(1, [path. "/", ''])
   call feedkeys("Arunt\<c-x>\<c-f>\<tab>\<cr>\<esc>", 'tnix')
   call assert_match('runtest\.vim', getline(1))
   %d