make sure right overload of PtrToStructure is called

Universally apply pawel's patch for cpymarsheltest.py

Signed-off-by: Tim Orling <TicoTimo@gmail.com>
runtests.py accepts parameter to select test subset
Merge pull request #6 from moto-timo/make-sure-right-overload-of-PtrToStructure-is-called

make sure right overload of PtrToStructure is called
cosmetic - consolidated PtrToStructure
added skip for all tests which crash unittest