Please don't import eventlet even if it's available

[gjcarneiro]

This code has two problems:

try:
    import eventlet
    try:
        from eventlet.green import urllib2 as eventlet_urllib2
    except ImportError:
        from eventlet.green.urllib import request as eventlet_urllib2
    has_eventlet = True
except:
    has_eventlet = False

1. Bare except: is evil, please catch a specific exception, ImportError in this case.
2. I am trying to get rid of eventlet in my code base, and so I have an assertion in my code: assert 'eventlet' not in sys.modules. Unconditionally importing eventlet makes it fail that assertion. Instead, could you please get the module only if it's already imported? if 'eventlet' in sys.modules: stuff.

[dcramer]

@gjcarneiro this is a standard practice for module detection. sys.module test would actually break if your code imported raven before eventlet.

That said, I'd be open to just not importing our eventlet code, ever. We can leave it up to the user at this point.

[autumnjolitz]

@gjcarneiro After you import raven, perhaps you could pop the eventlet off of sys.modules?