Improve MySQL support and export module.

[trans]

I added most of the types that MySQL supports (all the ones that are straight forward).

I also made the Export module a little more resilient. If a type is :none then it will still output the column but as a comment with :??? as the type. Maybe it should not output anything, but at least this way it would be easy to go back and find where fixes are needed by hand.

(Sorry about the four commits, not fully setup here yet so I had to do all this via the web.)

[trans]

So I spent more time with this and worked out the kinks. At this point I think it's in pretty good shape (at least the MySQL side of things). I was able to do a full schema generation for Fishbowl, which is a huge messy database, with no errors or warnings.