Mantis 2.0 - Database Layer Patch

This is a pull request to allow people to easily see the API changes [which previously have been welcomed by the other developers].

For now, this is purely here to allow comments on the syntax changes (that as I say, others have approved previously).

It is not a pull request to be merged into master in it's current form.

This patch replaces the ADODB database layer which is known-broken for
non-mysql database e.g. postgres, mssql, oracle in Mantis with a new layer
that:

a) provides supported postgres, mssql and oracle support within Mantis

b) Provides a php memory/performance increase over the existing database
layer for mysql users