DISPATCH-16: Integrated python error handling with dispatch logging and error handling.

See error.h, new function qd_error_py(). Checks for python error, logs python stack
trace and sets qd_error() indicators.

git-svn-id: https://svn.apache.org/repos/asf/qpid/dispatch/trunk@1602161 13f79535-47bb-0310-9956-ffa450edef68