fix: use local/custom enum for continuum operations

since we can't rely on that existing in rattail proper, due to it not
always having sqlalchemy

tailbone/diffs.py

@@ -27,8 +27,6 @@ Tools for displaying data diffs
 import sqlalchemy as sa
 import sqlalchemy_continuum as continuum
 
-from rattail.enum import CONTINUUM_OPERATION
-
 from pyramid.renderers import render
 from webhelpers2.html import HTML
 
@@ -272,11 +270,21 @@ class VersionDiff(Diff):
         for field in self.fields:
             values[field] = {'before': self.render_old_value(field),
                              'after': self.render_new_value(field)}
+
+        operation = None
+        if self.version.operation_type == continuum.Operation.INSERT:
+            operation = 'INSERT'
+        elif self.version.operation_type == continuum.Operation.UPDATE:
+            operation = 'UPDATE'
+        elif self.version.operation_type == continuum.Operation.DELETE:
+            operation = 'DELETE'
+        else:
+            operation = self.version.operation_type
+
         return {
             'key': id(self.version),
             'model_title': self.title,
-            'operation': CONTINUUM_OPERATION.get(self.version.operation_type,
-                                                 self.version.operation_type),
+            'operation': operation,
             'diff_class': self.nature,
             'fields': self.fields,
             'values': values,