Try rounding the values when resizing wxImage instead of truncating.

This would seem to make more sense and might also fix the test failures
resulting from tiny differences in arithmetic operations when compiled with
different compilers/under different architectures.

Regenerate the test files and commit (disabled) change to the unit test
allowing to do it again in the future.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75715 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775