Fix for size change graph construction
Fix for size change graph construction

Two things:
- No need to check the smaller thing is the same type; if it's an
  argument to a positive constructor, it's getting closer to the base.
  Just need to be sure it's not under a Delay
- 'Erased' is equal to anything, for various purposes, so need to be
  sure the thing we've found isn't 'Erased'

uuhan/Idris-dev,uuhan/Idris-dev,mpkh/Idris-dev,uuhan/Idris-dev,markuspf/Idris-dev,kojiromike/Idris-dev,FranklinChen/Idris-dev,markuspf/Idris-dev,kojiromike/Idris-dev,markuspf/Idris-dev,Heather/Idris-dev,FranklinChen/Idris-dev,Heather/Idris-dev,uuhan/Idris-dev,mpkh/Idris-dev,mpkh/Idris-dev,mpkh/Idris-dev,kojiromike/Idris-dev,FranklinChen/Idris-dev,markuspf/Idris-dev,markuspf/Idris-dev,Heather/Idris-dev,uuhan/Idris-dev,FranklinChen/Idris-dev,Heather/Idris-dev,Heather/Idris-dev,FranklinChen/Idris-dev,uuhan/Idris-dev,markuspf/Idris-dev,uuhan/Idris-dev,Heather/Idris-dev,markuspf/Idris-dev,kojiromike/Idris-dev,mpkh/Idris-dev,kojiromike/Idris-dev,mpkh/Idris-dev,kojiromike/Idris-dev,FranklinChen/Idris-dev