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"Unvisited" default: switch branch coverage

Goal: To join unvisited switch default: branch with earlier by compiler
inserted conditional branch.
Why? To cover in fact visited branch that is due compiler rewriting
reported as unvisited.
How: Branch instrumentation for all switch(default) and for all
conditional br instructions (if branch, not else branch!), where exists
unconditional-branch-jump-chain, is "pushed down". Last conditional jump
(if exists) is rewired to inserted instrumentation.