no_balance_collection.js failing on RHEL64

http://buildlogs.mongodb.org/Nightly%20Linux%20RHEL%2064-bit/builds/417/test/slow%20nightly/no_balance_collection.js

Looks like a timing issue. The function _lastMigration in src/mongo/shell/utils_sh.js is searching for any document in the changelog which starts with "moveChunk", but this includes both moveChunk.commit and moveChunk.from, so the assertion is failing even though the test is succeeding.