joesimms: initial draft for tree support. NestedSet support included, placeholders for other popular implementations also included. Read the README.tree file for more information and changelog to core files. Modified core files have also been included in this commit. hope it works and you like it !

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Doctrine now works seamlessly in multi-connection environment where connections are bound to classes

Updated some docs, added identifier quoting to DQL, fixed some test cases, fixed dql select part handling

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Ticket: 194

Ticket: 192

fixing #172 - copying a record now will set non-null fields to modified so that when it's saved it inserts correctly

Ticket: 150

Ticket: 150

Necessary changes to the validation components. Further improvements and docs will follow in the next days.
Ticket: 150

- validators codes are now string instead of integers (constants)
- validating is now handled in record level
- added new component Doctrine_Validator_ErrorStack
- new methods Doctrine_Record::isValid() and Doctrine_Record::getErrorStack()
- errorStack now as a record instance variable