Support both log4net 1.2.10 (old key) and later (new key) for Castle.Services.Logging

This changes the `Castle.Services.Logging.Log4netIntegration.dll` so it references two versions of log4net (yes, feel free to look at the code of how I did it, but Abandon hope all ye who enter here.

Bottom line is, this one assembly can support either old or new-key version of log4net (and possibly both at the same time if someone is insane enough to attempt that).

this requires importing the right namespace:
`using Castle.Services.Logging.Log4netIntegration;` for old-key version (so it's not a breaking change)
`using Castle.Services.Logging.Log4netIntegration.log4net2` for new-key version


Looking for some feedback, most of all - do we want to merge that? Does anyone foresee any potential problems with this change?