Removed hasattr() check, because hasattr() will call getattr() internally
anyway. If hasattr() fails, it means that getattr() has failed. So, there is no
need to call hasattr() before getattr().

Added error threshold to avoid infinite loops in parserengine.runengine().

Cython generated crappy and unstable code for py_callback, so I implemented the
py_callback method in C. This is easier to maintain and debug. This patch fixes
The random segfault caused by Python's garbage collector.