fpspreadsheet: Add test cases for insert/delete rows into worksheets containing formulas. Issues remaining when cells referred to by the formula are deleted. Add detection of error values to the formula scanner.

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3581 8e941d3f-bd1b-0410-a28a-d453659cc2b4