[Qt, OSX] fix Qt4.8 compatibility with QProgressBar issue
[Qt, OSX] fix Qt4.8 compatibility with QProgressBar issue

Rebased-From: 7f33d2cebfde99ded12c711ef6bd77c91725cfb8
Github-Issue: #5344

wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin