d-c-w-s causes an error when you provide as a type of a column
things like (string 5). I partially fixed it (it still throws an
unnecessary condition, but a good fix is srill necessary.

darcs-hash:51b1fc453b577a4a4ebd110606d77d136772e42b

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darcs-hash:03cc83f7913310863a606ba1d55c943613466151

No call to SQL-IZE in (add-constraint :around
(db-class-slot-definition)) caused many-to-many relations errors. Test
MANY-TO-MANY reproduces the bug.

darcs-hash:c26d8359f6838c05bc10b316a7efa6debf2a6e0f

darcs-hash:397ee7914e0dd3d01487b5f743f79617a638cf52

Now the order of class definitions is irrelevant: constrains that
could not be applied are delayed.

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darcs-hash:6594ffb37072223f70e09f9c5deb6bb6d6feabeb

Functions refering to non-transient slots now also reject slots whose allocation is :CLASS.

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darcs-hash:3e50766bd8901035d11e29520af841af53f3c7cb

Former WITH-CLASS-CONNECTION becomes, more appropriately,
WITH-OBJECT-CONNECTION. New macro WITH-CLASS-CONNECTION starts a
connection absing on a provided class.

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