Enhance error message

[mbaneshi]

Problem :

When we start bartib without specifying file in which activities will store ,
and run command , bartib stuck without any error message .

Solution :

bartib exist and show corresponding error.

hint :

Guide what bartib extension means.

[nikolassv]

This is strange. Normally, bartib should raise an error message saying:

Please specify a file with your activity log either as -f option or as BARTIB_FILE environment variable

In which environment do you use bartib?