FindGTK2: Add /usr/X11R6/ to include paths

Should fix builds on OpenBSD, see
http://open.cdash.org/viewTest.php?onlyfailed&buildid=3286713
Merge topic 'FindGTK2_fix_bsd' into next

ef9366b0 FindGTK2: Add /usr/X11R6/ to include paths
Merge topic 'target_compile_features'

9eaf3755 Export: Populate INTERFACE_COMPILE_FEATURES property.
8ed59fc2 Add target_compile_features command.
4e6ca504 cmTargetPropCommandBase: Change the interface to return bool.
5412dede cmTarget: Transitively evaluate compiler features.
baff4434 cmTarget: Allow populating COMPILE_FEATURES using generator expressions.
f97bf437 Features: Add cxx_auto_type.
03355d6b cmTarget: Add COMPILE_FEATURES target property.
faeddf64 project: Add infrastructure for recording CXX compiler features
913394af cmTarget: Add CXX_STANDARD and CXX_EXTENSION target properties.
8238a6cd Add some COMPILE_OPTIONS for specifying C++ dialect.
892243fc Tests: Require CMake 3.0 for the SystemInformation test.
59b5fdd3 Don't load Clang-CXX from AppleClang-CXX.
Merge topic 'cxx11-features'

60c0d2dd Features: Add cxx_defaulted_move_initializers.
c4e67235 Features: Add cxx_long_long_type.
dcaafada Features: Add cxx_func_identifier.
251a1f02 Features: Add cxx_local_type_template_args.
53fe7773 Features: Add cxx_extended_friend_declarations.
16603f7c Features: Add cxx_enum_forward_declarations.
adf22f61 Features: Add cxx_default_function_template_args.
7b3e8a05 Features: Add cxx_right_angle_brackets.
9a49fd21 Features: Add cxx_decltype_incomplete_return_types.
1889045c Features: Add cxx_sizeof_member.
ab455eba Features: Add cxx_thread_local.
300ce248 Features: Add cxx_inline_namespaces.
f9d04a96 Features: Add cxx_variadic_macros.
3d76656f Features: Add cxx_uniform_initialization.
e74b216c Features: Add cxx_generalized_initializers.
ff80c3b4 Features: Add cxx_attributes.
...
Merge branch 'master' into next