Do extra filtering in H300 (and H100) main unit button reading to suppress wrong...

Do extra filtering in H300 (and H100) main unit button reading to suppress wrong readings during voltage transitions. * Optimised multi-button ADC reads to use a balanced binary tree with an initial check for 'any button' to determine the pressed button. * The iriver button driver wouldn't have detected main unit (ADC-connected) buttons as long as remote buttons (ADC-connected) were pressed (btn = value; vs. btn |= value), * Do extra filtering in the recorder v1 OFF button read, to suppress spurious OFF events. * Some more tweaks.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@9530 a1c6a512-1295-4272-9138-f99709370657