change isWhitespace to table lookup
change isWhitespace to table lookup

$ repo/android.sh kati -c -kati_cpuprofile kati.prof

from (pprof) top30
before:
     560ms  2.88% 43.88%      560ms  2.88%  main.isWhitespace
     440ms  2.26% 51.28%      940ms  4.83%  main.(*wordScanner).Scan

after:
     540ms  2.87% 40.45%      540ms  2.87%  main.(*wordScanner).Scan

pombredanne/kati,shinh/kati,shinh/kati,dalinaum/kati,danw/kati,pombredanne/kati,colincross/kati,shinh/kati,dalinaum/kati,shinh/kati,danw/kati,colincross/kati,google/kati,colincross/kati,pombredanne/kati,google/kati,pombredanne/kati,colincross/kati,dalinaum/kati,colincross/kati,danw/kati,google/kati,colincross/kati,danw/kati,pombredanne/kati,pombredanne/kati,danw/kati,shinh/kati,dalinaum/kati,danw/kati,google/kati,shinh/kati,google/kati,dalinaum/kati