grace: fix compiliation against libpng 1.5

Library/Formula/grace.rb

@@ -1,22 +1,50 @@
 require 'formula'
 
 class Grace < Formula
-  url 'ftp://plasma-gate.weizmann.ac.il/pub/grace/src/grace5/grace-5.1.22.tar.gz'
   homepage 'http://plasma-gate.weizmann.ac.il/Grace/'
-  md5 '672356466f18fe59ed21a8fb44f9851d'
+  url 'ftp://plasma-gate.weizmann.ac.il/pub/grace/src/grace5/grace-5.1.22.tar.gz'
+  sha1 '3ce88c7c264d2de73b8935f835a1c1f8e368c78f'
 
   depends_on 'pdflib-lite'
   depends_on 'jpeg'
   depends_on 'fftw'
   depends_on 'lesstif'
 
+  # Upstream development has stopped, but we provide a minimal patch that
+  # allows compilation against libpng 1.5.
+  def patches
+    DATA
+  end
+
   def install
     ENV.x11
-
-    system "./configure", "--disable-debug", "--disable-dependency-tracking",
-      "--prefix=#{prefix}", "--with-zlib",
-      "--enable-grace-home=#{prefix}"
+    system "./configure", "--disable-debug",
+                          "--disable-dependency-tracking",
+                          "--prefix=#{prefix}",
+                          "--with-zlib",
+                          "--enable-grace-home=#{prefix}"
 
     system "make install"
   end
 end
+
+__END__
+--- a/src/rstdrv.c
++++ b/src/rstdrv.c
+@@ -54,6 +54,7 @@
+
+ #ifdef HAVE_LIBPNG
+ #  include <png.h>
++#  include <zlib.h>
+ #endif
+
+ #ifndef NONE_GUI
+@@ -885,7 +886,7 @@ static void rstImagePng(gdImagePtr ihandle, FILE *prstream)
+         return;
+     }
+
+-    if (setjmp(png_ptr->jmpbuf)) {
++    if (setjmp(png_jmpbuf(png_ptr))) {
+         png_destroy_write_struct(&png_ptr, &info_ptr);
+         return;
+     }