Added the NullAnalysis class to help bridge between the Beltime API,
which uses null analysis, and other APIs, which do not use null
analysis.

The remaining suppressed null analysis warnings have to do with the
inability to apply null analysis to fields in Eclipse 4.2 (Juno)
[https://bugs.eclipse.org/bugs/show_bug.cgi?id=331649].  Eclipse 4.3
(Kepler) adds support for null analysis of fields.  When we upgrade our
IDE to Kepler, we will address these warnings.