.clang-format: disable DerivePointerAlignment

everything outside of third_party should follow 'PointerAlignment:
right' i.e., associate the '*' with the variable

+ add a note about the clang-format that generated this file

Change-Id: I13e3f4f5fb6e22a8fa7fc3d06879c995b7c41a39
(cherry picked from libvpx e429080)

.clang-format

 ---
 Language:        Cpp
 # BasedOnStyle:  Google
+# Generated with clang-format 3.7.1
 AccessModifierOffset: -1
 AlignAfterOpenBracket: true
 AlignConsecutiveAssignments: false
@@ -28,7 +29,7 @@ ConstructorInitializerAllOnOneLineOrOnePerLine: false
 ConstructorInitializerIndentWidth: 4
 ContinuationIndentWidth: 4
 Cpp11BracedListStyle: false
-DerivePointerAlignment: true
+DerivePointerAlignment: false
 DisableFormat:   false
 ExperimentalAutoDetectBinPacking: false
 ForEachMacros:   [ foreach, Q_FOREACH, BOOST_FOREACH ]