grass: enable build on 10.9
gdal: tighten up caveats
Update grass.rb

If building head, the existing patch fails because the handling of Documentation in the install procedure is altered. This creates an alternate patch based on build.head? linked to a gist that removes the issue in a working manner.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
grass: updated patch for HEAD

Closes #23080.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>