Disable default checksum

[dcramer]

Per discussion in GH-125, we should disable the default client-side checksum (unless we're certain it's going to be better than the server can be). We should still provide the ability for the Event Builder to send checksums, it would just require user intervention.

[ColinHebert]

This behaviour has been corrected in July 2013:
41cda81

Patch already available in those versions:
v3.1 v3.1.1 v3.1.2 v4.1 v4.1.1 v4.1.2 v4.2 v5.0 v5.0.1

[ColinHebert]

The more general fix for the behaviour (not specific to message logs) is from April 2013:

4d99d5e

Every single version since v3.0 (since the entire rewrite), has this behaviour.

[ColinHebert]

All of that being said, based on the discussion in #125:

A hash must be a 32 character md5 checksum of the event

The current method we provide to generate a hash relies on CRC32 rather than md5, this can be fixed:
https://github.com/getsentry/raven-java/blob/v5.0.1/raven/src/main/java/net/kencochrane/raven/event/EventBuilder.java#L64

Could you give more details on how the said hash is generated (order of the arguments, etc.) so raven can produce a hash similar to the one provided by Sentry (if necessary)