Export as docx and xlsx instead of doc xls

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Backup to doc or xls

What is the expected output? What do you see instead?
Expected: file.doc and spreadsheet.xls
Instead: file.docx and spreadsheet.xls 

What version of the product are you using? On what operating system?
0.7.4.184

Please provide any additional information below.
docx and xlsx failed to open, they would open correctly only if I change the 
file extension to doc and xls manually .

Original issue reported on code.google.com by [email protected] on 25 Sep 2012 at 5:42