Improving constraint handling for Oracle databases

Hi,

I found that the handling of constraints for oracle Database doesn't work well in two scenarios:

   * you run the import as a user that doesn't own the tables. As original version used the USER_* elements of Oracle, it didn't find constraints for tables it didn't own. Therefore I used the ALL_* metadata tables of Oracle.
   * when importing only a subset of tables into a Schema, you need to disable the constraints on the *other* tables that reference the tables you'll import. Therefore the select clause got a bit more complicated.

In addition to that I would like to see some better error handling:

   * when there are problems re-enabling constraints, I want the program to enable as many constraints as possible before failing. This enables me to just fix the ones that fail afterwards.

The changeset includes all these changes. It ran nicely with my local (manual) tests; too bad you can't include an Oracle database in automatic tests.

I would be happy to see this in a maintenance release. 

Br Alexander.