Support Ecuador public RUC with juridical format

It seems that numbers with a format used for juridical RUCs have been
issued to companies.

Closes #457

Author: arthurdejong

stdnum/ec/ruc.py

@@ -99,8 +99,11 @@ def validate(number):
         except ValidationError:
             _validate_natural(number)
     elif number[2] == '9':
-        # 9 = juridical RUC
-        _validate_juridical(number)
+        # 9 = juridical RUC (or public RUC)
+        try:
+            _validate_public(number)
+        except ValidationError:
+            _validate_juridical(number)
     else:
         raise InvalidComponent()  # third digit wrong
     return number

tests/test_ec_ruc.doctest

@@ -288,6 +288,7 @@ Normal juridical RUC values (third digit is 9) that should just work.
 ... 1792141869001
 ... 1792147638001
 ... 1792373255001
+... 1793221293001
 ... 1890001323001
 ... 1890003628001
 ... 1890037646001