Fix EncodeInt implementation for power of 100 cases

Summary: The encodings were in violation of the SQLite4 spec due to the late trimming of trailing zeros.

Test Plan: updated unit tests

Reviewers: spencerkimball, jiangmingyang

Reviewed By: jiangmingyang

Subscribers: team

Differential Revision: http://phabricator.cockroachdb.org/D139