Don't rollback if exception is HTTPSuccessful or HTTPRedirection
In the request finishing, the 'cleanup' callback set by _cw_cnx
automatically commit the transaction except is an exception is set
on the request.
Problem is, redirections and successul http return code can raise
exceptions.
This patch detects such exceptions and avoid rolling back the transaction.
Closes #4566482
[pyramid\_cubicweb][] is one specific way of integrating [CubicWeb][] with a
[Pyramid][] web application.
### Features
* provides a default route that let a cubicweb instance handle the request.
### Usage
To use, install pyramid\_cubicweb in your python environment,
and then [include][] the package:
config.include('pyramid_cubicweb')
### Configuration
Requires the following [INI setting / environment variable][]:
* `cubicweb.instance` / `CUBICWEB_INSTANCE`
[pyramid\_cubicweb]: https://www.cubicweb.org/project/pyramid-cubicweb
[CubicWeb]: http://www.cubicweb.com/
[Pyramid]: http://pypi.python.org/pypi/pyramid
[include]: http://docs.pylonsproject.org/projects/pyramid/en/latest/api/config.html#pyramid.config.Configurator.include
[INI setting / environment variable]: http://docs.pylonsproject.org/projects/pyramid/en/latest/narr/environment.html#adding-a-custom-setting