Rescue from permission errors during reprocessing of thumbnails.

In my opinion, a permission error should not result in the entire
reprocessing job being terminated. Especially for large amounts of
files, it's to be expected one or two have various permission issues.

Instead of exiting, now simply print a warning to stderr.

lib/paperclip/attachment.rb

@@ -228,6 +228,9 @@ module Paperclip
       else
         true
       end
+    rescue Errno::EACCES => e
+      warn "#{e} - skipping file"
+      false
     end
 
     # Returns true if a file has been assigned.

test/integration_test.rb

@@ -34,6 +34,22 @@ class IntegrationTest < Test::Unit::TestCase
     should "create its thumbnails properly" do
       assert_match /\b50x50\b/, `identify "#{@dummy.avatar.path(:thumb)}"`
     end
+    
+    context 'reprocessing with unreadable original' do
+      setup { File.chmod(0000, @dummy.avatar.path) }
+      
+      should "not raise an error" do
+        assert_nothing_raised do
+          @dummy.avatar.reprocess!
+        end
+      end
+      
+      should "return false" do
+        assert ! @dummy.avatar.reprocess!
+      end
+      
+      teardown { File.chmod(0644, @dummy.avatar.path) }
+    end
 
     context "redefining its attachment styles" do
       setup do