Description of problem:
When the [X] button is clicked  in the BOINC Manager window's decoration, the applicaiton is minimized instead of exitted which doesn't conform to the standard behaviour and makes exitting BOINC Manager complicated.

Version-Release number of selected component (if applicable):
boinc-manager-7.0.65-2.git79b00ef.fc20.x86_64

How reproducible:
100 %

Steps to Reproduce:
1. run BOINC Manager
2. click on the [X] button in the top-right corner of its window

Actual results:
BOINC Manager minimizes

Expected results:
BOINC Manager exits or asks what to do (for the first time)

Additional info:
BOINC Manager was exitting when the [X] button was clicked back in F16 and maybe also F17.