Fix build failures.

The recent Query->join() changes contained an invalid column name, and
the changes to EntityContext necessitated changes in the tests to
reflect what should have always been reality.
Add note about identifier quoting in pdo error template.

Hopefully that should avoid a few unnecessary tickets.
Merge pull request #4030 from ADmad/3.0-pdo-error-msg

Add note about identifier quoting in pdo error template.
Merge pull request #4029 from cakephp/build-fix

Fix build failures.
Merge remote-tracking branch 'upstream/3.0' into 3.0
Simplify the purpose of the fullTableName method
While refactoring the fullTableName method, I realized that some Expressions (such as QueryExpression) and even Query object where wrapped in a TableNameExpression which was pointless.
This change simplifies the use of TableNameExpression : it now only wraps strings to prepend the prefix if needed.