Now grep and awk matchers doesn't waste buffer in case-sensisitive matching.
So I think that we can avoid line-by-line matching for them.

It enable to speed up case-sensitive matching with grep or awk matcher
without trivial_case_ignore as fast as when with it.

In bug#16232:
> The following times 2.16, 2.17 and 2.17+patch two ways:
> 
> $ yes jjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjjj | head -10000000 > k
> $ for i in 16 17 18; do echo $i; env LC_ALL=en_US.UTF-8 time
> /p/p/grep-2.$i/bin/grep -i foobar k; done
> 16
>        15.96 real        14.57 user         0.12 sys
> 17
>         1.13 real         1.07 user         0.06 sys
> 18
>         1.96 real         1.89 user         0.06 sys
> 
> The above search takes more than 70% longer with the proposed patch.

Therefore, I think 30% slow-down is caused by the line-by-line matching
for them.