Add @Nonnull and @Nullable annotations to the lexer package.

To be able to use findbugs to weed out problems in the HTML parser, we
need to tighten down its dependencies.  The lexer package is one of
these.

I added a package declaration for that package with a
@ParametersAreNonnullByDefault annotation, then ran findbugs and
whacked the null problems in that package.

This change also includes a bit of opportunistic cleanup of other
findbugs problems.


Submitted @4328

[MikeSamuel, 2010-11-03 17:55:09]

http://codereview.appspot.com/2864041/diff/1/build.xml
File build.xml (right):

http://codereview.appspot.com/2864041/diff/1/build.xml#newcode82
build.xml:82: <pathelement path="${third_party}/java/jsr305/jsr305.jar"/>
So javax.annotations can be used in tests.

[MikeSamuel, 2010-11-12 18:24:03]

ping

[Jasvir, 2010-11-18 18:42:44]

LGTM