all the "sub-directories" are pruned out in the output csv

[chinyeungli]

For intance, if I run the about.py on

tmp/t1/t2/test.ABOUT

The generated csv's about_file field will return
tmp/test.ABOUT

the t1/t2/ are pruned

[chinyeungli]

The problem is at
https://github.com/dejacode/about-code-tool/blob/master/about.py#L858

[chinyeungli]

@pombredanne I think this fix maybe a little bit "ugly", are you fine with it?