rename set_using_visited to set_using_irn_visited, some cosmetics, remove obsolete irflag functions from public headers

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[r17371]

- allocating helper data on an additional obstack that can be easily freed

[r17370]

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[r17368]

- allocating helper data on an additional obstack that can be easily freed
- fixed indentation
- moved ir_lopp generic functions to irloop.c

[r17367]

- allocating helper data an additional obstack that can be easily freed
- fixed indentation

[r17366]

[r17356]

[r17340]

- add missing skip_Proj()
- do not kill control flow from a dead block WITHOUT setting this block to dead
- fixed warning

[r17339]

when setting a block to dead, set its dom_depth to -1 to indicate that no dominance is avalable. It might not be possible to update the dom_info anymore!

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