winemac: Make clicking on the app's dock icon unminimize a window if there are only minimized windows.

Cocoa would automatically do this for a normal app.  However, the Mac driver
makes all of its windows inherit from NSPanel and Cocoa ignores panels for
this feature.

They show up in the taskbar on Windows 7.  Selecting them from there is
meaningful and useful, as is selecting them from the Window menu.

In addition to just switching among windows from that menu, this is also
important to recovering a minimized window if the user has configured their
system preferences to minimize windows into the process's dock icon (rather
than as separate dock icons).