Major rewrite of relational expressions and how property references are handled. Also added support for DbInExpression.
Added some tests for EF

A passing test only means it doesn't crash, not that it actually creates a correct SQL query.
Use the Text Output tab in NUnit to see the generated SQL queries, and verify that they are correct.
Removed unneeded constraint
Don't use Linq
Use a custom StringPair since Tuple is not available in .NET 3.5. Fix tests for pgsql <= 9.2.
Fix version tests.
Adding two test cases for EF from two bug reports.
Add parenthesis around || operator.
Fix parenthesis around left operand for IN
Fix merge conflict
Merge pull request #256 from Emill/master

Entity Framework: Fix relational expressions, column referencing, column name aliasing, implement DbApplyExpression and DbInExpression