core: fix crash when run from accentuated directory on windows
core: fix crash when run from accentuated directory on windows

function qi::program() did not always returned an utf8 encoded string,
and we got a boost::system_error when initializing qi::SdkLayout

FIXME:
 * add a test for this !
 * make SDKLayout crash when not built with a valid utf8
encoded prefix

bsautron/libqi,aldebaran/libqi,vbarbaresi/libqi,aldebaran/libqi,aldebaran/libqi