"is disconnect" codes with cx_oracle. [ticket:2864]

(e.g. for a ``CAST`` or similar) would incorrectly render ``None CHAR``
or similar. [ticket:2870]

if the synonym and the table were in different remote schemas.
Patch to fix courtesy Kyle Derr. [ticket:2853]

- add support for correlations to propagate all the way in; because
correlations require context now, need to make sure a select enclosure
of any level takes effect any number of levels deep.
- fix what we said correlate_except() was supposed to do when we first
released #2668 - "the FROM clause is left intact if the correlated SELECT
is not used in the context of an enclosing SELECT..." - it was not
considering the "existing_froms" collection at all, and prohibited
additional FROMs from being placed in an any() or has().
- add test for multilevel any()
- lots of docs, including glossary entries as we really need to define
"WHERE clause", "columns clause" etc. so that we can explain correlation better
- based on the insight that a SELECT can correlate anything that ultimately
came from an enclosing SELECT that links to this one via WHERE/columns/HAVING/ORDER BY,
have the compiler keep track of the FROM lists that correspond in this way,
link it to the asfrom flag, so that we send to _get_display_froms() the exact
list of candidate FROMs to correlate.  no longer need any asfrom logic in the
Select() itself
- preserve 0.8.1's behavior for correlation when no correlate options are given, not
to mention 0.7 and prior's behavior of not propagating implicit correlation more than one level..
this is to reduce surprises/hard-to-debug situations when a user isn't trying
to correlate anything.

Conflicts:
	doc/build/changelog/changelog_08.rst
	doc/build/changelog/changelog_09.rst
	lib/sqlalchemy/sql/compiler.py

- other cleanup
- don't need compat.decimal, that approach never panned out. hopefully
outside libs aren't pulling it in, they shouldn't be

to a DBLINK remote database; while the syntax has been present in the
Oracle dialect for some time, up until now it has never been tested.
The syntax has been tested against a sample database linking to itself,
however there's still some uncertainty as to what should be used for the
"owner" when querying the remote database for table information.
Currently, the value of "username" from user_db_links is used to
match the "owner".  [ticket:2619]

to use the cx_Oracle.LOB type when result rows are returned,
so the dialect has been repaired to exclude LONG from
having cx_Oracle.LOB filtering applied.  Also in 0.7.10.
[ticket:2620]

cx_Oracle so that a return value of ``False`` will result
in no call to ``connection.commit()``, hence avoiding
"no transaction" errors.   Two-phase transactions have
now been shown to work in a rudimental fashion with
SQLAlchemy and cx_oracle, however are subject to caveats
observed with the driver; check the documentation
for details.  Also in 0.7.10.
[ticket:2611]