Description of problem:
It is not possible to create a Unix mbox directory

Version-Release number of selected component (if applicable):
2.8.2.1

How reproducible:
the only option to set a path for a mbox directory is by using mouse clicks and
every time I click on a directory it opens it up, instead of choosing it.

Steps to Reproduce:
1. start evolution
2. click on edit->preferences->add account
3. select server type "standard mbox unix mbox spool or directory"
  
Actual results:
It does not allow me to select a directory as the path

Expected results:
Type the path for a unix mbox directory located in my local computer (old
messages) and create an account with messages sorted just as the folders located
in it. 

Additional info: