Menu and Desktop icon to launch an OSGeo4W command shell suitable for commandline utilities (GDAL, PROJ, etc).

• Installs osgeo4w.bat and creates link on Desktop
• installs bin\o-help.bat - a quick report of the available programs (pretty prints bin/*.exe, *.py)

Spawned from ticket #18

Changes

1.0.0-3 --> .0-4

• fixed bug in postinstall where duplicate desktop link was created

1.0.0-2 --> .0-3

• fixed bug in postinstall: Start menu one link was not created properly
• osgeo.bat calls o-help on startup
• Shortened osgeo-help.bat to o-help.bat (if you upgraded from .0-2 you may need to remove the old one manually)