Revert "splitSpaces: use bytes.IndexByte"
Revert "splitSpaces: use bytes.IndexByte"

Using bytes.IndexByte didn't help performance (probably because the
lines we were searching through were so short).  Commiting this and
then immediately reverting, so that its in the history in case this
proves useful in the future.

This reverts commit 15fd4e9d5c542d3e5d1751fd6971f57c7c050f1a.

bpowers/psm,bpowers/psm