Walk: Adding driver documentation plus some minor changes (ogr-walk-driver20130729.patch patch, #5169)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26228 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' of github.com:rouault/gdal into trunk_with_coverage