Install wx/preferences.h and wx/testing.h in "make install".

These headers were accidentally forgotten in files.bkl, add them there and
rebake.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76138 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Fix resource leak in wxMSW wxStaticBitmap when using RGBA icons.

Release the old handle if it wasn't freed by STM_SETIMAGE itself.

Closes #16068.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76141 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775