Added documentation: we can construct a PBQP instance which can not be solved heuristically if we removed some address mode patterns from our pattern set.
Added documentation: we can construct a PBQP instance which can not be solved heuristically if we removed some address mode patterns from our pattern set.

[r22929]

libfirm/libfirm,MatzeB/libfirm,8l/libfirm,killbug2004/libfirm,MatzeB/libfirm,MatzeB/libfirm,jonashaag/libfirm,jonashaag/libfirm,8l/libfirm,killbug2004/libfirm,jonashaag/libfirm,libfirm/libfirm,killbug2004/libfirm,8l/libfirm,davidgiven/libfirm,8l/libfirm,8l/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,davidgiven/libfirm,jonashaag/libfirm,jonashaag/libfirm,davidgiven/libfirm,8l/libfirm,davidgiven/libfirm,davidgiven/libfirm,davidgiven/libfirm,jonashaag/libfirm,killbug2004/libfirm,davidgiven/libfirm,libfirm/libfirm,killbug2004/libfirm,jonashaag/libfirm,8l/libfirm,killbug2004/libfirm,MatzeB/libfirm,MatzeB/libfirm,killbug2004/libfirm