Fixed XPath operator precedence.

Apparently using multiple `left` rules with T_AND and T_OR being separate
solves this problem. Riiiiight....

lib/oga/xpath/parser.y

@@ -12,7 +12,8 @@ options no_result_var
 
 prechigh
   left T_PIPE T_MOD T_DIV T_MUL T_SUB T_ADD
-  left T_GT T_GTE T_LT T_LTE T_NEQ T_EQ T_AND T_OR
+  left T_GT T_GTE T_LT T_LTE T_NEQ T_EQ
+  left T_AND T_OR
 preclow
 
 rule

spec/oga/xpath/parser/operator_precedence_spec.rb

@@ -105,9 +105,9 @@ describe Oga::XPath::Parser do
       parse_xpath('A and B = C').should == s(
         :path,
         s(
-          :eq,
-          s(:and, s(:test, nil, 'A'), s(:test, nil, 'B')),
-          s(:test, nil, 'C')
+          :and,
+          s(:test, nil, 'A'),
+          s(:eq, s(:test, nil, 'B'), s(:test, nil, 'C'))
         )
       )
     end