Execute default function of a MATLAB installation

Sometimes, we might want to "overload" a MATLAB method to change the behaviour of MATLAB.
It is then hard to call the default function again. The function "builtin" can only execute built-in, non-m-file functions.

This submission aims to mimic builtin() for m-files shipped with the MATLAB installation.

[y1, ..., yn] = defaultFunc(func, x1, ..., xn)

Calls the first function "func", which is found in MATLAB's installation directory, even if you placed a function with the same name somewhere in your search path.

func may be a string or a function handle.

It will *not* work with built-in functions, i.e. those without an m-file.
Use builtin( func, x1, ..., xn) for that case.

A usecase for this function is shown in
http://www.mathworks.com/matlabcentral/fileexchange/37971
which was the reason to create this submission.