[1.2.X] Fixed #13779 -- Can now discover GDAL 1.7 from debian-based packages. ...

[1.2.X] Fixed #13779 -- Can now discover GDAL 1.7 from debian-based packages.  Thanks to Leo for bug report and patch.

Backport of r13396 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13397 bcc190cf-cafb-0310-a4f2-bffc1f526a37