vim-patch:8.0.0545: edit test may fail on some systems

Problem:    Edit test may fail on some systems.
Solution:   If creating a directory with a very long path fails, bail out.
15ecbd6f3d

src/nvim/testdir/test_edit.vim

@@ -1324,22 +1324,31 @@ func Test_edit_quit()
 endfunc
 
 func Test_edit_complete_very_long_name()
-  if !has('unix') || has('mac')
+  if !has('unix')
     " Long directory names only work on Unix.
     return
   endif
+
+  let dirname = getcwd() . "/Xdir"
+  let longdirname = dirname . repeat('/' . repeat('d', 255), 4)
+  try
+    call mkdir(longdirname, 'p')
+  catch /E739:/
+    " Long directory name probably not supported.
+    call delete(dirname, 'rf')
+    return
+  endtry
+
   " Try to get the Vim window position before setting 'columns'.
   let winposx = getwinposx()
   let winposy = getwinposy()
   let save_columns = &columns
+  " Need at least about 1100 columns to reproduce the problem.
   set columns=2000
   call assert_equal(2000, &columns)
   set noswapfile
 
-  let dirname = getcwd() . "/Xdir"
-  let longdirname = dirname . repeat('/' . repeat('d', 255), 4)
   let longfilename = longdirname . '/' . repeat('a', 255)
-  call mkdir(longdirname, 'p')
   call writefile(['Totum', 'Table'], longfilename)
   new
   exe "next Xfile " . longfilename