Use vendored getargspec()

Use vendored getargspec()

Replaced the Python compatbility routines for ``getargspec()`` with a fully
vendored version based on ``getfullargspec()`` from Python 3.3.
Originally, Python was emitting deprecation warnings for this function in
Python 3.8 alphas.  While this change was reverted, it was observed that
Python 3 implementations for ``getfullargspec()`` are an order of magnitude
slower as of the 3.4 series where it was rewritten against ``Signature``.
While Python plans to improve upon this situation, SQLAlchemy projects for
now are using a simple replacement to avoid any future issues.

Change-Id: If5f3e2f6cc0df8d89e6c3035e024df3319964bf9
Fixes: #563