Just a warning, after cset 1d52db450db4 ishghandle.m has been removed.
However, there seems to be an issue with the way that the MXE process
builds and packages Octave for distribution. If you have been re-using a
directory for building MXE Octave then ishghandle.m will be present, but it
is now an untracked file. The installer happily bundles whatever files are
in the build directories and puts them in the final .exe or .zip. This
means that upon installation you will have both the new C++ version of
ishghandle and the old m-file version.
This won't happen if you clone a new MXE version for the build, or if you
do 'make clean', or if you remove ishghandle.m from your share directory
underneath the MXE directory.