Beginnings of force feedback support:
* Global functions needed to drive feedback state.
* HALHapticInterface abstract base class; support is advertised through HALGamePad::getHapticInterface().
* XInputHapticInterface implementation started.

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2551 86ba831e-150c-0410-ab35-e06eaae15ed9
* Remove cruft from i_system.h 
* m_dllist is not needed in i_gamepads.h

git-svn-id: http://mancubus.net/svn/hosted/eternity/trunk@2552 86ba831e-150c-0410-ab35-e06eaae15ed9