[Bridge] [Propel1] Fixed guessed relations

<table>
  <tr><th>Q</th><th>A</th></tr>
  <tr><td>Bug fix</td><td>yes</td></tr>
  <tr><td>Feature addition</td><td>no</td></tr>
  <tr><td>Backwards compatibility break</td><td>no</td></tr>
  <tr><td>Symfony2 tests pass</td><td>yes</td></tr>
  <tr><td>Fixes the following tickets</td><td>N/A</td></tr>
  <tr><td>Todo</td><td>N/A</td></tr>
  <tr><td>License of the code</td><td>MIT</td></tr>
  <tr><td>Documentation PR</td><td>N/A</td></tr>
</table>

The `PropelTypeGuesser` did not match OneToMany relations properly. For example if you have a `Author` class with `Comments` attributes the guesser would guess "Comment" instead of "Comments".

I added some tests to ensure the non regression.