Do not save weak references in Network by default (but use them for MagicNetwork)
Allow accessing objects in a Network via a dictionary-style interface, using the object's name
Also add an __iter__ method to support iterating directly over net (instead of iterating over net.objects)
Merge pull request #56 from brian-team/network_access

Network access
Always use numerical level values when setting the log levels (otherwise the logging system is broken in Python 2.6). Closes #57
Merge branch 'master' into devices