bug#14704286
SECONDARY INDEX UPDATES MAKE CONSISTENT READS DO O(N^2) UNDO PAGE
LOOKUPS (honoring kill query while accessing sec_index)

If secondary index is being used for select query evaluation and this
query is operating with consistent read snapshot it might take good time for
secondary index to return back control to mysql as MVCC would kick in.

If user issues "kill query <id>" while query is actively accessing
secondary index it will not be honored as there is no hook to check
for this condition. Added hook for this check.

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Parallely secondary index taking too long to evaluate for consistent
read snapshot case is being examined for performance improvement. WL#6540.