Update tests for Featureset iterator changes in 76c73ef0

[tomhughes]

No description provided.

[tomhughes]

These are the failures I was seeing without this:

======================================================================
ERROR: python_tests.postgis_test.test_threaded_create
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/builddir/build/BUILD/python-mapnik-541fd962d4fc99d50ec472af6ddccfdbf98cff37/test/python_tests/postgis_test.py", line 743, in test_threaded_create
    create_ds()
  File "/builddir/build/BUILD/python-mapnik-541fd962d4fc99d50ec472af6ddccfdbf98cff37/test/python_tests/postgis_test.py", line 732, in create_ds
    eq_(len(fs), 8)
TypeError: object of type 'Featureset' has no len()
======================================================================
ERROR: python_tests.postgis_test.test_psql_error_should_not_break_connection_pool
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/builddir/build/BUILD/python-mapnik-541fd962d4fc99d50ec472af6ddccfdbf98cff37/test/python_tests/postgis_test.py", line 970, in test_psql_error_should_not_break_connection_pool
    for feature in fs.features:
AttributeError: 'Featureset' object has no attribute 'features'

[lightmare]

Superseded by #140 (merged long ago)