Document how to build from git, and how to get jars from maven repo.

Document that we require maven 3.2, because of
https://jira.codehaus.org/browse/MNG-3385, fixed in maven 3.1.0-alpha-1.
That bug is minor, and maven 3.0 works fine for most purposes.

Add video links.
Add test case for [OPTIQ-411] duplicate column aliases
[OPTIQ-412] RelFieldTrimmer: when trimming SortRel, the collation and trait set don't match