[DBAL-592] Fix schema comparison with FK that contain quoted column names.

[Thinkscape]

In case QuoteStrategy decides to quote column names for FK, schema comparator (and in effect - schema tool), will be stuck in an ALTER TABLE * DROP FOREIGN KEY loop, because it doesn't recognise old indexes with matching column names.

The problem lies inside Comparator, which relied on column names that might or might not be quoted (depending on platform, schema and dbal settings). The comparison must be performed on unquoted column names both ways, as it is already performed for normal indexes, table names and columns names.

Tests will come shortly.

[doctrinebot]

Hello,

thank you for creating this pull request. I have automatically opened an issue
on our Jira Bug Tracker for you. See the issue link:

http://www.doctrine-project.org/jira/browse/DBAL-617

We use Jira to track the state of pull requests and the versions they got
included in.

[stof]

Can you add a test case covering this bug ?

[Thinkscape]

@stof Yeah, I'm on it. I'll try to derive from the setup I currently have...

[deeky666]

I think we should add Constraint::getUnquotedColumns() to the interface for consistency and make use of that. I added Constraint::getQuotedColumns() in 2.4 so I guess this BC break would be acceptable. Besides that there is already a Index::getUnquotedColumns() which does exactly the same.

[beberlei]

Merged into master and 2.4