Mac OS: the QPushButton hit area is not correct (too small)

The current "hit area" is too small and does not match the button. qt_mac_buttonIsRenderedFlat should always return true if another style than the mac style is detected.

Also when a style sheet is applied (to the push button or to its parent) the style of the push button becomes "QStyleSheetStyle" which creates confusion.

Included a test case to reproduce: main.cpp

Related commits:
http://qt.gitorious.org/qt/qt/commit/65a673f7ab1955e277246e4c88bec46493265cf3
http://qt.gitorious.org/qt/qt/commit/b0965cd049997283976c132fceb9727b6582ca49