Fix Unix build using clang with g++ 4.8 headers.

Don't override HAVE_TR1_TYPE_TRAITS detected by configure with
HAVE_TYPE_TRAITS detected by clang __has_include() as the latter is less
reliable and can return true even when the header is not actually usable, as
it happens with g++ 4.8 <type_traits> in non C++11 mode.

Closes #15915.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75985 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix harmless warnings about unused global variables.

Don't define variables that we never use to fix clang warnings about them.

See #15915.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75986 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove code maintaining last item from the treectrl sample.

The code was buggy (e.g. it didn't update the last item correctly after
executing "Append many items" menu command) and seems to be unnecessary.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75987 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove confusing delete from wxIdRangeManager dtor.

The singleton dtor shouldn't delete the global singleton object, if this were
ever really possible, it would result in an infinite recursion. And even
though it was not (because ms_instance was reset to NULL before destroying the
object pointed by it), this delete was still confusing and unnecessary, so
remove it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75988 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Improve parameter validation in wxStream code.

Replace wxASSERT_MSG()s with wxCHECK_MSG()s to ensure that we don't crash even
if we are passed a NULL pointer, saying "Warning: Null pointer is about to be
used" and crashing just isn't very useful in the grand scheme of things.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75989 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Always initialize values returned from wxGDDC::GetChar{Width,Height}().

Don't return garbage in case of error.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75990 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775