bounds check

git-svn-id: http://protostuff.googlecode.com/svn/trunk@1607 3b38d51a-9144-11de-8ad7-8b2c2f1e2016
default accessor like the rest

git-svn-id: http://protostuff.googlecode.com/svn/trunk@1608 3b38d51a-9144-11de-8ad7-8b2c2f1e2016
allow custom writer

git-svn-id: http://protostuff.googlecode.com/svn/trunk@1609 3b38d51a-9144-11de-8ad7-8b2c2f1e2016