ir: Do not print the irg in panic messages, if it is only available via current_ir_graph.
ircons: Use new_d_immBlock() to implement new_immBlock().
opt_confirms: Use get_irn_irg() instead of current_ir_graph.
iropt: Improve equivalent_node_Sync().

- Do not handle Bad. This is done by unreachable code elimination.
- Handle NoMem.
scalar_replace: Do not rely on current_ir_graph being set.

Use the _r variants of set_cur_block() and [gs]et_value().
all: Do not change current_ir_graph during walking/analyses/...