Move test file used by test polygon into same directory as the test

[ole]

The test test_polygon_function_csvfile currently relies on a test file 'mainland_only.csv' which resides outside the anuga code repository. Consequently, the test will fail on most installations (see output below). I suggest making a local copy of the test file in the same directory as test_polygon.py.

===================================================================== ERROR: test_polygon_function_csvfile (test_polygon.Test_Polygon)

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Traceback (most recent call last):

File "utilities\test_polygon.py", line 64, in test_polygon_function_csvfile

p1 = read_polygon(home+sep+'data'+sep+'western_australia'+sep+'dampier_tsunami_scenario_2006'+sep+'anuga'+sep+'polygons'

+sep+'2007polys'+sep+'mainland_only.csv') TypeError?: unsupported operand type(s) for +: 'NoneType?' and 'str'