[1.0.X] Now use `subprocess.Popen` instead of the deprecated os.popen3 to...

[1.0.X] Now use `subprocess.Popen` instead of the deprecated os.popen3 to issue PostGIS test database creation commands.

Backport of r9801 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9802 bcc190cf-cafb-0310-a4f2-bffc1f526a37