handle nicely typical installation other than debian package / mercurial forest * new _find_prefix method to detect installation prefix (maybe specified using CW_INSTALL_PREFIX environment variable) * set various resource accessors according to this, cleanup on the way * remove no more necessary APYCOT_ROOT hacks

When a TC failed to initiliase the database, the following test are SKIPPED When a TC failed to initiliase the database, the other test of the same TestCase are skipped with an explicite message instead of failing later for with an unrelated message.