fix some `go vet` errors
remove double spaces after full stop in comments
replace `go vet` by `go tool vet`: the latter works with files from different packages
Merge pull request #107 from tschottdorf/vetsyntax

A couple of no-brainer style fixes
Address Ben's feedback from PR #100
address Tobias' comments
Merge pull request #105 from cockroachdb/spencerkimball/address-bens-comments

Address Ben's feedback from PR #100
Enforce key length constraint of 2048 bytes.

Aside from needing to enforce a constraint of some sort, this change
allows us to definitively specify KeyMax, removing the previous requirement
that keys stored in the map couldn't start with \xff.
Addressed Tobias feedback, increased key size limit to 4096