pdf2svg: Fix Poppler dependency and download URL

Three changes:

- Download URL corrected.

- Now depends on pkg-config. Also depends on Cairo as poppler-glib requires
Cairo > 1.10, OS X 10.6.7 provides 1.8.6, and pkg-config needs the keg-only
formula to be on the PKG_CONFIG_PATH.

- Tests to see if Poppler was built with Glib support and offers a helpful
error message if this backend is missing.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Formula/pdf2svg.rb

@@ -1,14 +1,35 @@
 require 'formula'
 
+def have_poppler_glib?
+  # Not using Homebrew's system wrapper because we actually want to see the
+  # exit code of the command.
+  return Kernel.system "#{HOMEBREW_PREFIX}/bin/pkg-config", "poppler-glib", "--exists"
+end
+
 class Pdf2svg < Formula
-  url 'http://www.cityinthesky.co.uk/files/pdf2svg-0.2.1.tar.gz'
-  homepage 'http://www.cityinthesky.co.uk/pdf2svg.html'
+  url 'http://www.cityinthesky.co.uk/_media/opensource/pdf2svg-0.2.1.tar.gz'
+  homepage 'http://www.cityinthesky.co.uk/opensource/pdf2svg'
   md5 '59b3b9768166f73b77215e95d91f0a9d'
 
+  depends_on "pkg-config" => :build
+
   depends_on "poppler"
-  depends_on "gtk+" # Includes atk and cairo, through pango, if needed
+  depends_on "gtk+"
+  depends_on "cairo" # Poppler-glib needs a newer cairo than provided by OS X 10.6.x
+                     # and pdf2svg needs it to be on PKG_CONFIG_PATH during the build
 
   def install
+    unless have_poppler_glib?
+      onoe <<-EOS.undent
+        pkg-config could not find poppler-glib! Please try re-installing
+        Poppler with support for the Glib backend:
+
+            brew uninstall poppler
+            brew install --with-glib poppler
+      EOS
+      exit 1
+    end
+
     ENV.x11
     system "./configure", "--prefix=#{prefix}", "--disable-debug", "--disable-dependency-tracking"
     system "make install"