strstr, strcasestr speedup; add memmem

[Eric Blake]

According to Jeff Johnston on 1/11/2008 3:11 PM:
>> Here is an implementation that I recently wrote 
>> which uses the Two-Way algorithm [1] to guarantee O(m+n) operations 
>> while still only needing constant space
>>
>> OK to commit?
>>
> 
> Yes, thanks.

Thanks for the review.  After further testing on cygwin (I originally had
a bug in strcasestr if the match appeared at the beginning of the haystack
but with different case), I committed the corrected patch.

-- 
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9@byu.net