exportation of a database to Excel
[]=expbd2xls(bd,output,sheetname,transpose,names)
* bd = the name of a database or of a list of variables loaded in the environment
* output = the excel file where to save the data
* sheetname =the name of the sheet where the data are exported
* transpose = a boolean indicating whether the data should be transposed, i.e. presented in row (optional)
* names = the names to give to the data, if different from the name they have in Scilab (optional)
* nothing