Don't use the deprecated 'register' storage specifier.

It is not only useless with any modern C++ compiler, but also deprecated
in C++11.  Removing it fixes Clang warnings on the subject.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76582 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix wxOSX warnings about unused variables.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76583 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add missing Language: header to locale/msw/it.po.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76584 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
backport, fixing deletion of window during mouse down handler

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76586 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775