The "anonymize label" logic is now generalized to ClauseAdapter, and takes
place when the anonymize_labels flag is sent, taking effect for all
.columns lookups as well as within traverse() calls against the label
directly.
- traverse() will also memoize what it gets in columns, so that
calling upon traverse() / .columns against the same Label will
produce the same anonymized label.  This is so that AliasedClass
produces the same anonymized label when it is accessed per-column
(e.g. SomeAlias.some_column) as well as when it is applied to a Query,
and within column loader strategies (e.g. query(SomeAlias)); the
former uses traverse() while the latter uses .columns
- AliasedClass now calls onto ColumnAdapter
- Query also makes sure to use that same ColumnAdapter from the AliasedClass
in all cases
- update the logic from 0.9 in #1068 to make use of the same
_label_resolve_dict we use for #2992, simplifying how that works
and adding support for new scenarios that were pretty broken
(see #3148, #3188)

stringify a _label_reference() as is.
- add .key to _label_reference(), so that when _make_proxy()
is called, we don't call str() on it anyway.
- add a test to exercise Query's behavior of adding all the order_by
expressions to the columns list of the select, assert that things
work out when we have a _label_reference there, that it gets sucked
into the columns list and spit out on the other side, it's referred
to appropriately, etc.   _label_reference() could theoretically
be resolved at the point we iterate _raw_columns() but
it's better to just let things work as they already do (except
nicer, since we get "tablename.colname" instead of just "somename"
 in the columns list) so that we aren't adding a ton of overhead
to _columns_plus_names in the common case.

constructs are now importable from the "from sqlalchemy" namespace,
just like every other Core construct.
- The implicit conversion of strings to :func:`.text` constructs
when passed to most builder methods of :func:`.select` as
well as :class:`.Query` now emits a warning with just the
plain string sent.   The textual conversion still proceeds normally,
however.  The only method that accepts a string without a warning
are the "label reference" methods like order_by(), group_by();
these functions will now at compile time attempt to resolve a single
string argument to a column or label expression present in the
selectable; if none is located, the expression still renders, but
you get the warning again. The rationale here is that the implicit
conversion from string to text is more unexpected than not these days,
and it is better that the user send more direction to the Core / ORM
when passing a raw string as to what direction should be taken.
Core/ORM tutorials have been updated to go more in depth as to how text
is handled.
fixes #2992

- apply autopep8 + manual fixes to most of test/sql/

Found using: https://github.com/intgr/topy

of columns given positionally would not be preserved.   This could
have potential impact in positional situations such as applying the
resulting :class:`.TextAsFrom` object to a union.

Have also considered linking column.label() to the "column" itself being
in the result map but this reveals some naming collision problems (that
also seem to be very poorly tested...).   This should be as far as
we want to go right now with [ticket:2932].

- get PG dialect to work around "no nonexistent binds" rule for now,
though we might want to reconsider this behavior