InputWrapper: add a GUIGetButtonDown function, which behaves the same as GetButtonDown but is meant to be called from OnGUI. Will reliably return true only once per frame.
InputWrapper: add an optional parameter to GetPressedAxis (and CaptureInput) to disallow capturing of mouse movement.
GUIF: Consolidate SButton overloads by using optional parameters.
GUIF: Allow specification of a control to click an SButton, rather than requiring any specific control to always be present.
GUIF: SButton uses GUIGetButtonDown in InputWrapper for detecting its control.
GUIF: A selected SButton will not be clicked if space bar is pressed (workaround for a Unity bug, http://issuetracker.unity3d.com/issues/pressing-the-space-bar-also-presses-the-currently-focused-gui-button ), unless Space is the "select" control.