Implement whole tuple constraints in addition to field constraints.
They are quite similar to field constraints, the difference is:
 * The are set in space options instead of format field definition.
 * Entire tuple is passed to check function.
 * By design field constraints are a bit more optimal.

One can set up constraint in space options, with one or several
functions that must be present in _func space:
box.schema.space.create(.. {.. constraint='func1'})
box.schema.space.create(.. {.. constraint={name1='func1'})
box.schema.space.create(.. {.. constraint={name1='f1', name2='f2'})

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