title: Flask-Migrate hangs on table modificiation
body: <p>I have an issue on running the upgrade command with Flask-Migrate.  Originally I was trying to modify three tables at once and it hung, I narrowed it down to a specific table (the other upgrades worked without issue).  I don't see any locks on the database.  I'm using Postgres and just working in a development environment at the moment.  The migrate command seems to work fine and generates the <code>upgrade</code> method without any issues (see code)</p>
  
  <pre><code>def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.drop_column('equipment', 'criteria_notes')
      # ### end Alembic commands ###
  </code></pre>
  
  <p>Once I run the upgrade command I get stuck here:</p>
  
  <pre><code>&gt;flask db upgrade
  INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
  INFO  [alembic.runtime.migration] Will assume transactional DDL.
  INFO  [alembic.runtime.migration] Running upgrade 76bf72d8e0e4 -&gt; 1723c01f0606, empty message
  </code></pre>
  
  <p>with a blinking cursor.  When I exit out of the command window (I'm using windows) no changes have been applied.</p>
  
  <p>I've tried</p>
  
  <ul>
  <li>Restarting computer </li>
  <li>Looking for locks or other sessions with pgAdmin</li>
  <li>Modifying other tables, was able to add and drop columns</li>
  </ul>