Improve performance consistency with LIKE and % operator

[bronwyncombs]

I still see an odd distinction in the timings for a LIKE search - the %hello search takes much longer than the hello% search.

LIKE.search.compare.mp4

Context: 1.3 million rows in query.

Confirmed in tests on herb-rbge (1.6 mil CO), v7.12.0.6 and v7.12.0.6-csiro.

Reported by Dan @ CSIRO (BoldDesk 1060)