Thanks Marc Tamlyn for the report and Ian Foote/Tim Graham for review.

As CharField.to_python() now always calls str(), assigning bytes to a
CharField is no longer correct usage. Doing so results in a warning:

  django/db/models/fields/__init__.py:1061: BytesWarning: str() on a bytes instance

Use a unique constraint violation to trigger the database error instead.

Warning introduced in 301de774.

Lookup right hand side processing was compiling query compilers which happened
to work by chance as SQLCompiler defines a as_sql() method with two optional
parameters albeit it doesn't expect the same type of arguments.

Thanks Preston Timmons for review.

Thanks Tim Graham for the review.

Regression in f5c62957.

This reverts commit e62ea0bb since it
broke multi-column __in lookups and _meta.order_wrt on Oracle.

Django's test runners no longer discover doctests.

Queries could potentially be resolved in cases where ordering matter.

Thanks Tim Graham for the review.

The is_iterator() function was removed in 2456ffa4.

read() and write() were removed in 68a890e7.