Tests fail on Windows

[dkfellows]

Some tests include an assumption about the directory separator that are invalid on Windows in at least some configurations.

Example:

======================================================================
FAIL: test_too_few (make_tools.test_file_convert.TestConverter)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Users\Donal\git\SpiNNUtils\unittests\make_tools\test_file_convert.py", line 168, in test_too_few
    FileConverter.convert(src, dest, "too_few.c")
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 626, in convert
    FileConverter()(source, destination, file_id, log_database)
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 133, in __call__
    if not self._process_line(dest_f, line_num, text):
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 175, in _process_line
    return self._process_line_normal_code(dest_f, line_num, text)
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 321, in _process_line_normal_code
    return self._process_line_in_log(dest_f, line_num, text[start_len:])
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 247, in _process_line_in_log
    self._write_log_method(dest_f, line_num)
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 457, in _write_log_method
    short_log = self._short_log(line_num)
  File "c:\users\donal\git\spinnutils\spinn_utilities\make_tools\file_converter.py", line 420, in _short_log
    raise Exception(
Exception: Too few parameters in line "test %f %i", -1.0f); at 19 in C:\Users\Donal\git\SpiNNUtils\unittests\make_tools\mistakes\too_few.c

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\Donal\git\SpiNNUtils\unittests\make_tools\test_file_convert.py", line 173, in test_too_few
    self.assertIn("mistakes/too_few.c", str(ex1))
AssertionError: 'mistakes/too_few.c' not found in 'Too few parameters in line "test %f %i", -1.0f); at 19 in C:\\Users\\Donal\\git\\SpiNNUtils\\unittests\\make_tools\\mistakes\\too_few.c'

I do not think this is a significant failure; it's just looking for the wrong thing.