Fix javadoc warnings

[sslavic]

Before this fix there were numerous javadoc warnings being reported
while building Spring framework API.

This fix resolves most of the javadoc warnings.

Issue: SPR-9113

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[sslavic]

@cbeams I will change title and description of this pull request, rebase it to latest master and also align javadoc changes with your comment.

Since pull request contains lots of changes (all only for numerous warnings reported when building api), would it be easier for validation and accepting the pull request to split it somehow or is single pull request with everything OK?

Would be great if pull request 35 was accepted first. Have to adjust pull request description there.

[cbeams]

A single pull request is ok, as long as individual commits in the PR represent distinct atomic changes.

I can merge #35 first, that's fine. Rebase them if you like, but if I don't get to merging it right away, I'll rebase it again locally before committing anyway.

[cbeams]

This is merged, thanks Stevo. Please note however that a couple modifications were necessary:

• a number of the changed lines had trailing whitespace. This is probably an artifact of your editor. Consider making whitespace visible while editing ("Show Whitespace Characters" in Eclipse); or just examine carefully the output of git diff before pushing commits. If you have color diffs enabled, you'll see trailing whitespace in red.
• Apache copyright headers were not updated in most files, i.e. 2002-2011 being updated to 2002-2012.

Both of the above are covered in the contributor guidelines.

This is a big improvement; it reduced the number of javadoc warnings from 265 to 103. Thanks again!