refreshed contributor agreement from open plans

Signed-off-by: Jody Garnett <jody.garnett@gmail.com>
fix release guide warnings

Signed-off-by: Jody Garnett <jody.garnett@gmail.com>
fix broken references in security programming instructions

Signed-off-by: Jody Garnett <jody.garnett@gmail.com>
Merge pull request #294 from jodygarnett/developers_guide_fixes

Updated contributor agreement and fix a few developers guide warnings
Merge branch 'master' of git://github.com/geoserver/geoserver