Corrected XPath operator precedence.

The previous commit didn't fully change the operator precedence according to
the XPath 1.0 specification. Also thanks to @whitequark for clearing up a few
things about Racc's operator precedence system.

lib/oga/xpath/parser.y

@@ -12,8 +12,10 @@ 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
-  left T_AND T_OR
+  left T_LT T_LTE T_GT T_GTE
+  left T_EQ T_NEQ
+  left T_AND
+  left T_OR
 preclow
 
 rule

spec/oga/xpath/parser/operator_precedence_spec.rb

@@ -94,9 +94,9 @@ describe Oga::XPath::Parser do
       parse_xpath('A or B and C').should == s(
         :path,
         s(
-          :and,
-          s(:or, s(:test, nil, 'A'), s(:test, nil, 'B')),
-          s(:test, nil, 'C')
+          :or,
+          s(:test, nil, 'A'),
+          s(:and, s(:test, nil, 'B'), s(:test, nil, 'C'))
         )
       )
     end
@@ -116,9 +116,9 @@ describe Oga::XPath::Parser do
       parse_xpath('A = B < C').should == s(
         :path,
         s(
-          :lt,
-          s(:eq, s(:test, nil, 'A'), s(:test, nil, 'B')),
-          s(:test, nil, 'C')
+          :eq,
+          s(:test, nil, 'A'),
+          s(:lt, s(:test, nil, 'B'), s(:test, nil, 'C'))
         )
       )
     end