[Takusen] Takusen package split and source re-org

[oleg at okmij.org]

> I'd like to resume work on Takusen, a little at a time

Excellent!

> Regarding (1): people have said that it's wrong for Takusen to have a
> setup that changes the API depending on what you have installed, and
> I'm inclined to agree. 

That is true, yet there is a reason for that: different back-end do
have different ways of connecting to the database -- different API for
connecting. There are many other subtle differences between
databases. Certainly we may gloss over them; after all, all relational
DBMS support a fair share of common SQL. One can do a lot using only
that common functionality. Yet, if one deals with large databases or
requires fast answers to queries, one has to become familiar with
idiosyncrasies of a particular DBMS. The ability to use
database-specific functions may be crucial at some times. If we don't
provide it, the whole Takusen package becomes useless then. It is
indeed a challenge how to unify different back-ends and yet preserve
their differences for the cases where they matter.

The new Repo structure indeed looks much nicer than before. I only
have the comment on test/Test/, which contains general unit testing
framework. It could well be a separate Hackage package, or even part
of Haskell Platform. I would have put 
	Test/MiniUnit.hs 
	Test/MiniUnitTest.hs
under core/src. 

	Cheers,
	Oleg