Work on Unit Tests + Mono

Hi again Francisco.

Here's a pull request that fixes some problems in the unit test SQL init scripts - take a look at these (do these scripts actually work for you?).

Also added the MonoNotSupported NUnit category which excludes the System.Transaction tests, at least for now (I've just submitted a pull request to mono to add support for this). However, like you said there are still many failing tests (nothing to do with mono apparently).

Once you decide what to do with the xmlModel generated tests (how to exclude for mono, or just disable them for now?) I think you'll have a fully functioning mono-friendly xbuild system.