Catch SSL and HTTPErrors and retry at most 3 times, after, raise the exception

[s0undt3ch]

Refs #339.

[s0undt3ch]

I was able to trigger the timeout once using my cloned fork of raven.
This is a small workaround, though, I've been unable to repeat my ssl read errors.

[coveralls]

Coverage decreased (-0%) when pulling 698dcf4 on s0undt3ch:master into d201373 on getsentry:master.

[dcramer]

I dont recall if we prevent you from submitting the same event twice (based on an event id), but if not this would cause you to submit it repeatedly in real-world situations.

This also would cause people to DDOS getsentry.com as soon as they hit a 429 (rate limited error), which is likely an HTTPError.

Realistically I dont think this is a good solution to "my webserver timed out". It's just log data, and there will be more of it. If the timeout is the problem we should address that, or if you're hosting your own Sentry you should enable the cache + queue.