wibox.widget.textbox: skip setting unchanged layout properties

In case the text, markup or other layout properties have not changed, there's
no need to update the widget.

Based on 5a2a5d03d3/lib/wibox/widget/textbox.lua.
Closes https://github.com/awesomeWM/awesome/pull/335.

lib/wibox/widget/textbox.lua

@@ -58,10 +58,15 @@ end
 --   `<b>bold</b>`). You can use awful.util.escape to escape
 --   parts of it.
 function textbox:set_markup(text)
+    if self._markup == text then
+        return
+    end
+
     local attr, parsed = Pango.parse_markup(text, -1, 0)
     -- In case of error, attr is false and parsed is an error message
     if not attr then error(parsed) end
 
+    self._markup = text
     self._layout.text = parsed
     self._layout.attributes = attr
     self:emit_signal("widget::updated")
@@ -70,6 +75,10 @@ end
 --- Set a textbox' text.
 -- @param text The text to display. Pango markup is ignored and shown as-is.
 function textbox:set_text(text)
+    if self._layout.text == text and self._layout.attributes == nil then
+        return
+    end
+    self._markup = nil
     self._layout.text = text
     self._layout.attributes = nil
     self:emit_signal("widget::updated")
@@ -80,6 +89,9 @@ end
 function textbox:set_ellipsize(mode)
     local allowed = { none = "NONE", start = "START", middle = "MIDDLE", ["end"] = "END" }
     if allowed[mode] then
+        if self._layout:get_ellipsize() == allowed[mode] then
+            return
+        end
         self._layout:set_ellipsize(allowed[mode])
         self:emit_signal("widget::updated")
     end
@@ -90,6 +102,9 @@ end
 function textbox:set_wrap(mode)
     local allowed = { word = "WORD", char = "CHAR", word_char = "WORD_CHAR" }
     if allowed[mode] then
+        if self._layout:get_wrap() == allowed[mode] then
+            return
+        end
         self._layout:set_wrap(allowed[mode])
         self:emit_signal("widget::updated")
     end
@@ -100,6 +115,9 @@ end
 function textbox:set_valign(mode)
     local allowed = { top = true, center = true, bottom = true }
     if allowed[mode] then
+        if self._valign == mode then
+            return
+        end
         self._valign = mode
         self:emit_signal("widget::updated")
     end
@@ -110,6 +128,9 @@ end
 function textbox:set_align(mode)
     local allowed = { left = "LEFT", center = "CENTER", right = "RIGHT" }
     if allowed[mode] then
+        if self._layout:get_alignment() == allowed[mode] then
+            return
+        end
         self._layout:set_alignment(allowed[mode])
         self:emit_signal("widget::updated")
     end