Add FIXME.
Remove commented-out code.
Update comment on suspected bug in SplitAfterCall.
Remove broken merging of previously split blocks.

Merging and thus deleting the current basic block invalidates the iterator.
Apart from that this is what the SimplifyCFG pass already implements.
Add TODO for signature checks in normal blocks.
Add TODO about code duplication in InstrumentBasicBlocks::instrumentBasicBlock().
Merge branch 'cleanup' into develop