Add flushing close to places that deal with exceptions so that the order
of lines in the output reflect the order of execution for the
corresponding print statements.
The actual buffering behavior differs depending on the Python
interpreter version used, which led to spurious diffs with older
versions.
TN: W306-034
Since the analysis context initialization may trigger events (e.g.
"prelude file parsed"), language bindings (in particular Python) may
need to create/register their wrapper around the context that is just
created so that they can use that wrapper when invoking the callback.
Having allocation and initialization as a single atomic step makes this
impossible: this change splits them in the C API and update the
Python/OCaml bindings to allow this.
TN: VA12-016
