Refined the valgrind log-munger.

Let .ingest() eat arbitrarily many files; now returns a tuple of Report
objects. A few corrections to simple mistakes in the first pass, a TODO comment
and related code-change, tuple() a list on return, assorted comments to help the
reader.
Track leakage cleared and return it from .repair()
Support ignoring stacks that contain a given frame.

Reorganised support for marking a stack as repair()ed so as to unify
with its implementation.
Made leak's size details into a vector.

Fixed a typo in vector.py while I was at it.

Reworked .repair()'s reporting of leak size saved to work with the
vector size of leaks.  Leak now needs .sure as a property, recovered
from the size information.