- The system of loader options has been entirely rearchitected to build
upon a much more comprehensive base, the :class:`.Load` object.  This
base allows any common loader option like :func:`.joinedload`,
:func:`.defer`, etc. to be used in a "chained" style for the purpose
of specifying options down a path, such as ``joinedload("foo").subqueryload("bar")``.
The new system supersedes the usage of dot-separated path names,
multiple attributes within options, and the usage of ``_all()`` options.
-  Added a new load option :func:`.orm.load_only`.  This allows a series
of column names to be specified as loading "only" those attributes,
deferring the rest.

- rework the event system so that event modules load after their
targets, dependencies are reversed
- create an improved strategy lookup system for the ORM
- rework the ORM to have very few import cycles
- move out "importlater" to just util.dependency
- other tricks to cross-populate modules in as clear a way as possible

ideas in general:
  - pypy2.1 w/ sqlite3 is the first DBAPI we're seeing returning
    unicode in cursor.description without being py3k.  add a new on-connect
    check for this, if we get back a u"", just don't do description decoding,
    should be OK for now.
  - the set tests in test_collection were assuming the two sets would be ordered
    the same when it tested pop(), can't really assume that.
  - test_serializer gets worse and worse, pickle is just not really viable here,
    ding out pypy
  - pypy2.1b2 seems to allow cursor.lastrowid to work (or we changed something?)
  - pool._threadconns.current() is a weakref, it can be None
  - another one of those logging.handlers imports

- clean up inspect() calls within query._join()
- make sure join.alias(flat) propagates
- fix almost all assertion tests

- went through examples/ and cleaned out excess list() calls

added, which proxies down to the ``.info`` attribute on either
the :class:`.schema.Column` object if directly present, or
the :class:`.MapperProperty` otherwise.  The full behavior
is documented and ensured by tests to remain stable.
[ticket:2675]

mapper configuration; will now test for name conflicts on
superclasses and subclasses, in addition to the current mapper,
as these conflicts break things just as much.  This is new for
0.8, but see below for a warning that will also be triggered
in 0.7.11.
- Improved the error message emitted when a "backref loop" is detected,
that is when an attribute event triggers a bidirectional
assignment between two other attributes with no end.
This condition can occur not just when an object of the wrong
type is assigned, but also when an attribute is mis-configured
to backref into an existing backref pair.  Also in 0.7.11.
- A warning is emitted when a MapperProperty is assigned to a mapper
that replaces an existing property, if the properties in question
aren't plain column-based properties.   Replacement of relationship
properties is rarely (ever?) what is intended and usually refers to a
mapper mis-configuration.   Also in 0.7.11.
[ticket:2674]

- paths now store Mapper + MapperProperty now instead of string key,
so that the parent mapper for the property is known, supports same-named
properties on multiple subclasses
- the Mapper within the path is now always relevant to the property
to the right of it.  PathRegistry does the translation now, instead
of having all the outside users of PathRegistry worry about it,
to produce a path that is much more consistent.  Paths are now
consistent with mappings in all cases.  Special logic to get at
"with_polymorphic" structures and such added also.
- AliasedClass now has two modes, "use_mapper_path" and regular;
"use_mapper_path" is for all those situations where we put an AliasedClass
in for a plain class internally, and want it to "path" with the
plain mapper.
- The AliasedInsp is now the first class "entity" for an AliasedClass,
and is passed around internally and used as attr._parententity
and such.  it is the AliasedClass analogue for Mapper.

  1. all Comparators now have "parent" which is always the parent mapper
  or AliasedClass instance

  2. only RelationshipProperty.Comparator has "mapper" now, which
  is the target mapper

  3. The names "parententity" and "parentmapper" are underscored

also improved the message with the "neither comparator nor instruentedattribute...."
to include the classname + attribute name