Added names for some theme related windows messages
Fixed grab interaction with Windows Classic theme

Testing:
* For each theme in Windows 7, Windows 7 Basic, and Windows 7 Classic:
- Ran testsprite2
- Pressed Ctrl-G to grab the mouse
- Alt-tabbed away, verified mouse is no longer grabbed
- Alt-tabbed back, verified that mouse was grabbed
- Alt-tabbed away
- Clicked in the window, verified mouse was grabbed
- Alt-tabbed away
- Grabbed the title bar and dragged the window around successfully, verified that mouse was grabbed when move modal loop completed
- Alt-tabbed away
- Clicked the minimize button on the title bar, the window was successfully minimized
- Clicked on the icon in the task bar, the window was restored and the mouse grabbed again
- Alt-tabbed away
- Clicked the close button on the title bar, the window was successfully closed