Add a number of tests for the dev-tools. The tests iterate over all .xls
files that are found under test-data, any newly added file or
code-change which breaks one of the dev-tools will cause the tests to
fail in the future. Known broken files can be excluded.

Also fixes two points where some files could cause BiffViewer to fail.

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1535885 13f79535-47bb-0310-9956-ffa450edef68