stack cache analysis: Spill Cost Analysis graph and major cleanup

* clean up comments and code -- use consistent terms, yeah!
* summarize worst-case occupancy of call-sites using a function
  local analysis
* propagate stack occupancy on call graph using worst-case occupancy
  and context-sensitive occupancy information from callers
* store analysis result in spill cost analysis graph (SCA graph)
* minor pruning of SCA graph
patmos: stack cache analysis stats and extensions

* keep track of various statistics
* extend ILP to search for shortest/longest tail for displacement