bug fix for CHR-30

see: http://jira.palaso.org/issues/browse/CHR-30

This fixes an issue encountered by one of our users who received a crash in chorus while trying to push up their FLEx project to LD for the very first time.  The repo size being pushed up was about 450 MB.  There was an arithmetic overflow exception thrown in the resumable transport code when calculating the time remaining.

This pull request fixes the bug (for bundle sizes < 2GB) and adds a regression test.