Mark dangerous multiple-table updates as destructive queries

[gfrlv]

MySQL allows to update multiple tables at once, like this:

update foo, bar
set foo.a = 1, bar.b = 2
where bar.b = 1

The table for which there is no where-clause is specified will be updated completely. We now warn about complete table updates (issue #728, resolved in #785), but the current realization only works with the one-table form.

[scottnemes]

@rolandwalker This would be a good one to be done at some point. Basic idea is it needs to parse what tables are in the update clause, and then verify that all of those tables (or aliases) are referenced in the where clause. The latter is the more difficult part since columns in the where clause may not have a table reference at all, which makes verifying them more tricky.

[rolandwalker]

Good find!