Improve UPDATE queries with JOINs

[mindplay-dk]

UpdateQuery currently does not quote column-references - this could lead to collisions in multi-table update-queries where columns in different tables have identical names.

Ideally, quoting column-references should be done conditionally, e.g. only in update-queries that actually have joins.

[mindplay-dk]

UpdateQuery currently does not quote column-references

This is incorrect: column references are definitely quoted, though perhaps I meant qualified, which they are not - but qualifying would be required only in multi-table updates, which aren't supported by the UPDATE statement in most databases, including Postgres.

While multi-table updates are supported in MySQL, I wouldn't count this as a bug, just a non-feature.

As this feature is very non-standard, and has some odd limitations in MySQL (which you can read about in the manual), I'm not going to support it at this time.