fpspreadsheet: Make sure that biff writers do not write colors exceeding the maximum palette count. Add casse to error tests (passed, but the biff2 font color test fails now...)

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3470 8e941d3f-bd1b-0410-a28a-d453659cc2b4