Case insensitive matching of nodes

This re-applies the patch added in #134 to the new XPath compiler.

Fixes #135.

lib/oga/xpath/compiler.rb

@@ -1398,9 +1398,12 @@ module Oga
         ns, name = *ast
 
         condition = nil
+        name_str  = string(name)
+        zero      = literal(0)
 
         if name != STAR
-          condition = input.name.eq(string(name))
+          condition = input.name.eq(name_str)
+            .or(input.name.casecmp(name_str).eq(zero))
         end
 
         if ns and ns != STAR

spec/oga/xpath/compiler/paths_spec.rb

@@ -16,6 +16,12 @@ describe Oga::XPath::Compiler do
       end
     end
 
+    describe '/A' do
+      it 'returns a NodeSet' do
+        evaluate_xpath(@document).should == node_set(@a1)
+      end
+    end
+
     describe '/' do
       it 'returns a NodeSet' do
         evaluate_xpath(@document).should == node_set(@document)