Fixed comparing node equality in XPath expressions

Previously this would take the text of the entire node set, not of the first
node in the set.

lib/oga/xpath/evaluator.rb

@@ -724,11 +724,11 @@ module Oga
         right = process(ast_node.children[1], context)
 
         if left.is_a?(XML::NodeSet)
-          left = left.text
+          left = first_node_text(left)
         end
 
         if right.is_a?(XML::NodeSet)
-          right = right.text
+          right = first_node_text(right)
         end
 
         if left.is_a?(Numeric) and !right.is_a?(Numeric)

spec/oga/xpath/evaluator/operators/eq_spec.rb

@@ -46,5 +46,13 @@ describe Oga::XPath::Evaluator do
     example 'return true if a node set and a string are equal' do
       @evaluator.evaluate('root/a = "10"').should == true
     end
+
+    example 'return true if a node set wildcard and a number are equal' do
+      @evaluator.evaluate('root/* = 10').should == true
+    end
+
+    example 'return true if a number and a node set wildcard are equal' do
+      @evaluator.evaluate('10 = root/*').should == true
+    end
   end
 end