Document --prereqs and --debug in scansys.py lead-in comments.
Fix a handful of glitches and infelicitous names in scansys.py.

You know you were hacking too late last night when you get up the next
morning and discover you committed an incomplete merge.
Refactor scansys.py with an engine class.

The functions that do all the real work no longer have five or more state
arguments threaded through them.
Add compiler-identification annotation to scansys output.
Document scansys's absolute pathname requirement.

Also document scansys's need to work with py2.0 in README.md, and shuffle
the code around a little so all the compatibility kludges are at the top.
Better auto-labeling of new inventory files.
scansys.py now labels dependent and buggy headers.

Update inventorying instructions accordingly.
Flush data files generated with an old scansys.py.
Add freshly generated inventories for Linux (glibc 2.13)