emlinecat_new.py fails when using --npixmin with only one threhsold

[Christian Herenz]

Apparently the renumbering of the object IDs is not handled correctly in this case.

#!
Traceback (most recent call last):
  File "../Knusper2000-muse-python-d40039ad4078/emlinecat_new.py",
line 530, in <module>
    assert max_label == label_cube.max()
AssertionError

Running with 2 thresholds (-t and -T) does not produce the error.

[Christian Herenz]

--npixmin switch has been removed and now only a single threshold is used. note also emlinecat_new.py has been replaced by lsd_cat.py