Blacklight::Solr::Document#to_param should return a string to work wi…

…th rails routing.

Fixes #638

lib/blacklight/solr/document.rb

@@ -114,7 +114,7 @@ def id
   end
 
   def to_param
-    id
+    id.to_s
   end
 
   def as_json(options = nil)

spec/helpers/url_helper_spec.rb

@@ -225,6 +225,13 @@ def params
       @document = SolrDocument.new('id'=>'123456')
       expect(link_to_document(@document,:label=>"Some crazy long label...")).to_not match(/title=/)
     end
+
+    it "should  work with integer ids" do
+      data = {'id'=> 123456 }
+      @document = SolrDocument.new(data)
+      expect(link_to_document(@document)).to have_selector("a")
+    end
+
   end
 
   describe "link_to_previous_search" do

spec/lib/blacklight/solr/document_spec.rb

@@ -44,6 +44,14 @@ def my_extension_method
         @document = MockDocument.new :id => 'asdf', :my_unique_key => '1234'
         expect(@document.id).to eq '1234'
       end
+
+    end
+
+    describe "#to_param" do
+      it "should be a string" do
+        @document = MockDocument.new :id => 1234
+        expect(@document.to_param).to eq '1234'
+      end
     end
 
     context "Extendability" do