abiword: fails_with :clang, update patches

* Devel patches no longer apply; seems to need none
* Add a libpng patch, required on all OS X versions
* fails with clang; need to test on 425

Fixes Homebrew/homebrew#17513.

Formula/abiword.rb

@@ -20,14 +20,20 @@ class Abiword < Formula
   depends_on 'wv'
   depends_on 'imagemagick'
 
-  def patches
-    if build.devel?
-      {:p0 => "http://bugzilla.abisource.com/attachment.cgi?id=5477"}
-    else
-      DATA
-    end
+  fails_with :clang do
+    build 421
+    cause "error: static_cast from 'id' to 'XAP_Menu_Id' (aka 'int') is not allowed"
   end
 
+  def patches
+    {
+      # Fixes newer libpng versions; needed for libpng 1.2, too
+      :p0 => "https://trac.macports.org/export/102401/trunk/dports/editors/abiword-x11/files/patch-libpng-1.5.diff",
+      # Fixes bad glib include
+      :p1 => DATA
+    }
+  end if build.stable?
+
   def install
     system "./configure", "--disable-debug", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"