Class jxl.write.biff.WritableWorkbookImpl

Added interface jxl.biff.formula.ExternalSheet.

Added Methods
int getExternalSheetIndex(String)	Gets the external sheet index for the sheet name
String getExternalSheetName(int)	Gets the name of the external sheet specified by the index
BOFRecord getWorkbookBof()	Parsing of formulas is only supported for a subset of the available biff version so we need to test to see if this version is acceptable