Enable storing an SXSSF workbook twice

Verify this via a unit-test for all types of workbooks
Add a test to verify the contents is byte-for-byte equal
Also remove an overwritten test which works the same now for all three workbook-types

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1886060 13f79535-47bb-0310-9956-ffa450edef68
3 files changed