asm: correct wrong index name
analysis: add #if to make pmode exactly match non-pmode

This switch will throw away the hard work of some worker thread, so it should
only be used for debugging.

With the flag enabled, pmode matches non-pmode output exactly for RD levels
2, 3 and 4. But RD 5 and 6 still have problems.
analysis: clarify --rd 1
analysis: do not allow top-skip and depth earlyout in --pmode with --rd 5/6

Now outputs match or are better than those without --pmode
search: nits - pull Mode out of Search class, remove unused NUM_LAYERS
cmake: remove obsolete pool test
Merge with stable
analysis: inline checkBestMode(), improve comments