Fix length constraints on text fields

Use TEXT type for ImportTaskMessage model fields that may contain
values longer than 256 characters.

galaxy/main/migrations/0123_fix_importtaskmessage_constraints.py

@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.17 on 2018-12-13 13:47
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('main', '0122_auto_20181015_1802'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='importtaskmessage',
+            name='message_text',
+            field=models.TextField(),
+        ),
+        migrations.AlterField(
+            model_name='importtaskmessage',
+            name='rule_desc',
+            field=models.TextField(null=True),
+        ),
+    ]

galaxy/main/models.py

@@ -719,9 +719,7 @@ class ImportTaskMessage(PrimordialModel):
         max_length=10,
         choices=constants.ImportTaskMessageType.choices(),
     )
-    message_text = models.CharField(
-        max_length=256,
-    )
+    message_text = models.TextField()
     is_linter_rule_violation = models.NullBooleanField(
         default=False,
     )
@@ -737,8 +735,7 @@ class ImportTaskMessage(PrimordialModel):
         max_length=256,
         null=True,
     )
-    rule_desc = models.CharField(
-        max_length=256,
+    rule_desc = models.TextField(
         null=True,
     )
     rule_severity = models.IntegerField(