Support for Partial Indexes for PostgreSql and Sqlite

Support for Partial Indexes was available in Doctrine 1 following
http://www.doctrine-project.org/jira/browse/DC-82. This commit
reintroduce support for Doctrine 2. We use the same syntax with an
optionnal "where" attribute for Index and UniqueConstraint.
Refactor partial into options array

This coherent with what is done for Table. All platform specific things
are grouped into an options array. Eventually flags should be migrated
into options as well.
Adapt formatting to pre-existing content
Surround ! with spaces according to code style
Merge pull request #1027 from PowerKiKi/feature-partial-indexes

Support for Partial Indexes for PostgreSql and Sqlite
Ensure metadata cache is not ArrayCache in production
Code style fixes.
Fix namespace collission
Merge pull request #1177 from c960657/production-settings-arraycache

Ensure metadata cache is not ArrayCache in production
Test case for merging entities with associations to identical entities.
Fix merging of entities with associations to identical entities.

Without this patch, when an entity that refers multiple times to the same
associated entity gets merged, the second references becomes null.

The main issue is that even though doMerge returns a managed copy, that value
is not used while cascading the merge. These identicial entities are already
detected through the visitor map, but they are ignored.  There should be some
refactoring so cascadeMerge calls a function that checks if the parent must be
updated, based on the return value of its call to doMerge.  However, this patch
tries to impact the code as little as possible, and only introduces a new
function to avoid duplicate code.

The secondary issue arises when using inverted associations. In that case, it
is possible that an entity to be merged is already merged, so the the visitor
map is looked up by the hash of a managed copy instead of the original entity.
This means that in this case the visitor map entries should also be set to the
entity, instead of being set to 'true'.
#1173 - applying CS fixes on top of the patch
#1173 - test CS fixes, reduced clutter code, made method names more explicit
Merge branch 'hotfix/#1173-merge-association-to-identical-entities'

Close #1173
Don't load detached proxies when merging them.

Ticket DDC-1392 fixed an issue where uninitialized proxies could not be merged
because the merge routine couldn't get the identifier from them. The soution
was to initialize the proxy.
Ticket DDC-1734 fixed the merging of *unserialized* uninitialized proxies by
resetting their internals, so these proxies were able to initialize, as required
by the fix for DDC-1392.

Somehow, in the meanwhile, the fix for DDC-1392 is not needed anymore:
reverting the patch will not break the associated test (but it does break the
test for DDC-1734). This means it is not needed anymore to initialize the proxy
when merging.

Uninitialized proxies that get merged should not be loaded at all.  Since they
are not initialized, the entity data for sure hasn't changed, so it can be
safely ignored. Actually, the only thing the data is needed for while merging,
is to copy it into the managed entity, but that one is already supposed to be
up to date. By not initializing the proxy, a potential database roundtrip is
saved, and the fix for DDC-1734 is not needed anymore.

Besides optimizing the merge, this patch also solves an issue with merging.
Currently, when a detached uninitialized proxy is merged while there is already a
corresponding managed entity (proxy or not), the ORM returns a blank entity
instead of returning the already managed entity. This patch makes sure that
already existing managed entities are re-used.