updated SEXTANTE documentation
Merge branch 'master' of https://github.com/qgis/QGIS-Documentation
Updated Dutch preamble.po and foreword.po
Dutch translation for help_and_support.po. Minor fixes for foreword.po and conventions.po
Merge pull request #56 from milovanderlinden/master

Updated preamble.po and foreword.po for dutch translation
update context menu