Expand @property(class) declaration to support older versions of Xcode.
Expand @property(class) declaration to support older versions of Xcode.

@property(class) was added in Xcode 8; by explicitly declaring the
setAllowsAutomaticWindowTabbing accessor, we can continue building
with Xcode 6.2.

0branch/qtide,0branch/qtide,0branch/qtide