Add support for SO numbers

Adds the possibility of using SO numbers when registering in GREG.

greg/tests/test_utils.py

@@ -12,12 +12,12 @@ def test_so_number():
 def test_not_allow_so_number():
     so_number = "25529312345"
     settings.ALLOW_SO_NUMBERS = False
-    assert is_valid_id_number(so_number) == False
-    assert is_valid_so_number(so_number) == False
+    assert not is_valid_id_number(so_number)
+    assert not is_valid_so_number(so_number)
 
 
 def test_not_valid_so_number():
     so_number = "25529322345"
     settings.ALLOW_SO_NUMBERS = True
-    assert is_valid_id_number(so_number) == False
-    assert is_valid_so_number(so_number) == False
+    assert not is_valid_id_number(so_number)
+    assert not is_valid_so_number(so_number)