Initial DDEX support : new pr

A new pull request.
Initial DDEX support code is inherited from #67 started by wwindcloud.

DDEX tips:
- DDEX support will work on VS2012/VS2013 Pro (VS2013 needs [Visual Studio 2013 Update 2 RC](ttp://www.microsoft.com/en-us/download/confirmation.aspx?id=42307) or later)
- Specify all of Host, Username, Password and **Database** properties in DDEX connection dialog.
- Capture your ConnectionString for later use. For example,
```
PORT=5432;TIMEOUT=15;POOLING=True;MINPOOLSIZE=1;MAXPOOLSIZE=20;COMMANDTIMEOUT=20;COMPATIBLE=2.1.0.0;HOST=127.0.0.1;USER ID=npgsql_tests;PASSWORD=npgsql_tests;DATABASE=npgsql_tests
```

Built tips:
- Open *Npgsql2012.sln*.
- Configuration: *Debug-net45*, *Release-net45* or such.
- Built the entire solution.
- Install the generated vsix. For example, NpgsqlDdexProvider\bin\Debug-net45\NpgsqlDdexProvider.vsix
- gacutil /i  Npgsql.dll