Adding MySQL and Mongo slave functionality

[smchugh]

Here is a patch to add in MySQL functionality along with a few other things we needed.

Changes:

• Copy to MySQL instead of Postgres, which includes adapter-specific error handling
• Column options (null, index, default)
• Reading from a Mongo replica slave

Thanks for taking a look.

[nelhage]

Thanks for the patchset! I'm super busy right now, but I'll try to look at this in more detail by early next week at the latest.

[smchugh]

Thanks for taking a look at this. The Travis CI error seems to be from the fact that it's looking for 0.3.1 rather than 0.3.2. I'll change the version file to use 0.3.1 when I go in and remove the slaveOk commit

[nelhage]

I'm fine taking this PR if you fix the things I've mentioned. I'd ideally like to see the code factored out so we have backend-specific adapters that implement a common interface, but I'm happy to merge this for now without that.

[goutamdan]

During the initial import, the query for bulk copying always fails because of syntax errors caused by wrong quoting. The field names have double quotes and the values have no quotes at all. So this always falls back to the update and insert queries. This makes initial import extremely slow. Any plans to fix this?

[smchugh]

@goutamdan We ended up not using this tool, so the projected ended up dropped. I'd ideally like to pick it back up on my own time, but haven't had the chance. If you wanted to pick this up, I'd be more than glad to accept a PR into this branch.

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