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The expressions have that type.

Also add a GRAPH_PROPERTY for the analysis state.

- Setting dep edges to NULL is illegal now
- add_irn_dep is simpler but does not check for duplicates anymore

Get away from the strange set_default_XXX_op style and instead let the
code modules register their node ops directly.

This also supports setting the initial node number to "rand", thereby
replacing randnodenr.