removed eclipse warnings. updated maven plugins to the latest versions

git-svn-id: http://google-gson.googlecode.com/svn/trunk@1307 2534bb62-2c4b-0410-85e8-b5006b95c4ae
fixed issue 469 by adding a TypeAdapterFactory for throwables that ignores cause if it is self-referencing

git-svn-id: http://google-gson.googlecode.com/svn/trunk@1308 2534bb62-2c4b-0410-85e8-b5006b95c4ae
added tests for Throwable. Revised ReflectiveTypeAdapterFactory to ignore self-referencing fields.

git-svn-id: http://google-gson.googlecode.com/svn/trunk@1309 2534bb62-2c4b-0410-85e8-b5006b95c4ae