Remove log10 from boost in prefix search

Because nothing but number of incoming links effects the score removing
the log10 from boost sorts the results the same way while doing less work.

On itwiki this amounts for going from 200ms for a prefix search for "a"
to 60ms.  Even though these are cached most of the time this is worth it.

Change-Id: Ifc60f466f324161b2349aecbe1312aef7993d172
Merge "Remove log10 from boost in prefix search"