Fix url_for options[:subdomain] to allow objects as values

* e.g. blog_url(subdomain: current_user) instead of blog_url(subdomain: current_user.to_param)

dbconsole: Use the app's database_configuration instead of duplicating loading code.

With transactional fixtures enabled, the session records would end up in
@_current_transaction_records, and at the end of the transaction,
methods would be called on them that would trigger method_missing and
trigger attribute methods to be generated.

However, at this point the sessions table would not exist, and the
columns were not cached, so an exception would be raised because we
can't find the columns to generate attribute methods for.

Not sure exactly why this didn't crop up before but there have been
changes to the schema cache code and perhaps that means that column data
that was cached previously at that point is now uncached.

It was a bad idea to rescue exceptions here. This can interfere with
transaction rollbacks which seems to be the cause of current CI
failure.

Instead, each adapter should implement its own DB-specific O(1)
implementation, and we fall back on the generic, slower, implementation
otherwise.

log exception backtrace when all backtrace lines silenced

missing require in buffered logger

Add config.file_watcher so developers can provide their own watchers (for instance, hooking on fsevents).

commented whitelist mode enforcement for mass assignment

missing require in activesupport test

This reverts commit c2e3ce8d.

Conflicts:

	railties/lib/rails/application/configuration.rb
	railties/lib/rails/application/finisher.rb
	railties/lib/rails/engine.rb

Fixes #3957

Use rubygems https endpoint for the Gemfile on new apps