FIX: Removed widgets would incorrecly retain capture permamently.
FIX: Removed widgets would incorrecly retain capture permamently.

This only really was an issue in multi GUIContext set ups, but basically
gave a situation where capture could never be released because once
detached, the window reverts to the default GUIContext (which is not the
one that the widget captured input for).

cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two,cbeck88/cegui-mirror-two