Now mode_b behaves the same as integer modes, so use the same code to initialize the special values.

The removed special case used the same color anyway.

The new code in bitop_chain did not consider Add nodes that behaved like
logical ops.

Note that for OO code you should use liboo which provides the same
features!

The rule that a rule becomes undefined if it has an undefined input is
only true if the node has no side effects.

This fixes opt/combo7.c

This fixes opt/fehler227.c.

Also clean up the macro.

The empty string is a prefix of everything.

Only let ir_should_dump() succeed, if the filter is a prefix of the name, not the other way round, too.