Bug finder: Report #7

[Aaron Tomb]

Accomplished this week:
* Finished support for NonNull attributes on method, properties,
fields, and parameters. Attributes can be read from assemblies or
from a file listing the entities they apply to (useful for defining
the interface of a library without modifying it).
* Tweaked the null dereference analysis in a number of ways to reduce
false positives.
* Tested null dereference analysis more heavily.
* Slightly changes the possible abstract values variables can take in
the null dereference dataflow.
* Added copyright notices to everything.
* Fixed miscellaneous bugs.

Problems I encountered:
* Nothing very serious.

Plans for next week:
* More testing.
* Investigating other potential checks to perform.
* Cleaning up source code.
* Investigating exceptions once again.

I'm at a point now where I'm not entirely sure what I want to do next. I
don't know whether I want to focus more on adding new checks, or on
improving the accuracy of the checks that are already present. The
nature of the forms of analysis I'm doing means that the accuracy will
never be perfect, but tweaks of one sort or another can almost always
improve it.

If there's anyone on this list who is interested in using this tool, I'd
like to know what you'd most like out of it. Also, for Miguel, if
differences in the direction I take for next week will affect
acceptance, let me know about that, too.

If I get no feedback, I'll probably spend the remaining time tweaking
and cleaning up what I have, and wait until after the Summer of Code is
over to add significant new features.

Aaron