Improve the error message for when #ifndef guards don't match the #define.

Patch from <csharp@google.com>

diff --git a/cpplint/cpplint.py b/cpplint/cpplint.py
index 016116b..c985c5d 100755
--- a/cpplint/cpplint.py
+++ b/cpplint/cpplint.py
@@ -1071,12 +1071,18 @@
       endif = line
       endif_linenum = linenum
 
-  if not ifndef or not define or ifndef != define:
+  if not ifndef:
     error(filename, 0, 'build/header_guard', 5,
           'No #ifndef header guard found, suggested CPP variable is: %s' %
           cppvar)
     return
 
+  if not define:
+    error(filename, 0, 'build/header_guard', 5,
+          'No #define header guard found, suggested CPP variable is: %s' %
+          cppvar)
+    return
+
   # The guard should be PATH_FILE_H_, but we also allow PATH_FILE_H__
   # for backward compatibility.
   if ifndef != cppvar:
@@ -1089,6 +1095,12 @@
     error(filename, ifndef_linenum, 'build/header_guard', error_level,
           '#ifndef header guard has wrong style, please use: %s' % cppvar)
 
+  if define != ifndef:
+    error(filename, 0, 'build/header_guard', 5,
+          '#ifndef and #define don\'t match, suggested CPP variable is: %s' %
+          cppvar)
+    return
+
   if endif != ('#endif  // %s' % cppvar):
     error_level = 0
     if endif != ('#endif  // %s' % (cppvar + '_')):
diff --git a/cpplint/cpplint_unittest.py b/cpplint/cpplint_unittest.py
index 9903bc9..361629a 100755
--- a/cpplint/cpplint_unittest.py
+++ b/cpplint/cpplint_unittest.py
@@ -2054,7 +2054,7 @@
     self.assertEquals(
         1,
         error_collector.ResultList().count(
-            'No #ifndef header guard found, suggested CPP variable is: %s'
+            'No #define header guard found, suggested CPP variable is: %s'
             '  [build/header_guard] [5]' % expected_guard),
         error_collector.ResultList())
 
@@ -2067,7 +2067,7 @@
     self.assertEquals(
         1,
         error_collector.ResultList().count(
-            'No #ifndef header guard found, suggested CPP variable is: %s'
+            '#ifndef and #define don\'t match, suggested CPP variable is: %s'
             '  [build/header_guard] [5]' % expected_guard),
         error_collector.ResultList())