small reworking of the loop-breaker-choosing algorithm

Previously inline candidates were given higher preference as
non-loop-breakers than constructor applications, but the reason for
this was that making a wrapper into a loop-breaker is to be avoided at
all costs.  This patch refines the algorithm slightly so that wrappers
are explicitly avoided by giving them a much higher score, and other
inline candidates are given lower scores than constructor
applications.

This makes almost zero difference to a complete nofib run, so it
amounts to just a tidyup.