'shortmess': Add "F" flag. #4446

Add "Don't give the file editing message" flag in shortmess option.

Add the UI tests by @fmoralesc
Fix the changes for Vim 7.4.1570

test/functional/ui/shortmess_spec.lua

@@ -0,0 +1,40 @@
+local helpers = require('test.functional.helpers')
+local Screen = require('test.functional.ui.screen')
+local clear, feed, execute = helpers.clear, helpers.feed, helpers.execute
+
+describe("'shortmess'", function()
+  local screen
+
+  before_each(function()
+    clear()
+    screen = Screen.new(25, 5)
+    screen:attach()
+    execute('set shortmess&')
+  end)
+
+  after_each(function()
+    screen:detach()
+  end)
+
+  describe("=F", function()
+    it(':hides messages about the files read', function()
+      execute('e test')
+      screen:expect([[
+        ^                         |
+        ~                        |
+        ~                        |
+        ~                        |
+        "test" is a directory    |
+      ]])
+      execute('set shortmess=F')
+      execute('e test')
+      screen:expect([[
+        ^                         |
+        ~                        |
+        ~                        |
+        ~                        |
+        :e test                  |
+      ]])
+    end)
+  end)
+end)