[FIX] tests: Fix test errors when running with numpy 1.13.0

[ales-erjavec]

Issue

3 test failures when running with numpy 1.13.0

======================================================================
FAIL: test_init_inst (Orange.tests.test_instance.TestInstance)
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Traceback (most recent call last):
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\Orange\tests\test_instance.py", line 170, in test_init_inst
    dtype=object))
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\numpy\testing\utils.py", line 854, in assert_array_equal
    verbose=verbose, header='Arrays are not equal')
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\numpy\testing\utils.py", line 778, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Arrays are not equal
(mismatch 33.33333333333333%)
 x: array([0, nan, 42.0], dtype=object)
 y: array([0, nan, 42], dtype=object)
======================================================================
FAIL: test_init_xym_no_data (Orange.tests.test_instance.TestInstance)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\Orange\tests\test_instance.py", line 82, in test_init_xym_no_data
    dtype=object))
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\numpy\testing\utils.py", line 854, in assert_array_equal
    verbose=verbose, header='Arrays are not equal')
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\numpy\testing\utils.py", line 778, in assert_array_compare
    raise AssertionError(msg)
AssertionError: 
Arrays are not equal
(mismatch 66.66666666666666%)
 x: array([nan, nan, ''], dtype=object)
 y: array([nan, nan, ''], dtype=object)
======================================================================
FAIL: test_reprable (Orange.tests.test_util.TestUtil)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Miniconda35\conda-bld\orange3_1497021380284\_t_env\lib\site-packages\Orange\tests\test_util.py", line 50, in test_reprable
    "ReplaceUnknownsRandom("
AssertionError: "Repl[62 chars]_of_decimals=3), distribution=Continuous([[ 0.],      [ 0.]]))" != "Repl[62 chars]_of_decimals=3), distribution=Continuous([[ 0.], [ 0.]]))"
- ReplaceUnknownsRandom(variable=ContinuousVariable(name='x', number_of_decimals=3), distribution=Continuous([[ 0.],      [ 0.]]))
?                                                                                                                    -----
+ ReplaceUnknownsRandom(variable=ContinuousVariable(name='x', number_of_decimals=3), distribution=Continuous([[ 0.], [ 0.]]))

Description of changes

• Remove use of assert_array_equal for object arrays
• Compare the Reprable output ignoring whitespace.

Includes

• Code changes
• Tests
• Documentation