Delete old EF6
Upgraded to EF6.0.1
Reorganized Entity Framework support

- Reorganized the code into three projects/packages:
  1) The Npgsql "core", fully functional ADO.NET and no EF
  2) Npgsql.EntityFramework, an add-on for users of EF6 and above
  3) Npgsql.EntityFrameworkLegacy, an add-on for users of EF5 and below
- All EF-related code has been split off from Npgsql and into
  the Npgsql.EntityFramework directory
- The same EF code is built via two projects: Npgsql.EntityFramework
  (defining ENTITIES6 for the new EF6), and Npgsql.EntityFrameworkLegacy
  (not defining it for pre-EF6).

Still to be done:
- Npgsql.NpgsqlFactory doesn't yet do the reflection work to return the
  pre-EF6 NpgsqlServices
- Only the 2013 sln is up to date
- nuspecs
My fix to get EdmGen/EdmGen06 and my EFv6 app working.

Tested on:
- Windows 7 Home Premium SP1 64-bit
- 3 assemblies got into gac.
  Debug-net45\Npgsql.dll
  Debug-net45\Npgsql.EntityFramework.dll
  Legacy-Debug-net45\Npgsql.EntityFrameworkLegacy.dll
- machine.config modified.
- my EFv6 app's App.config modified.
More tweaks to EntityFramework support

- Tightened some details in the reflection loading of EntityFrameworkLegacy
  (thanks kenjiuno)
- Did nuspecs entity framework projects
- Corrected SLNs for 2012, 2010
Fix for System.IO.FileNotFoundException in NpgsqlFactory.GetService

Rewrote assembly and type resolving better.
Fixed the strategy how to approach Npgsql.EntityFrameworkLegacy.

If you request DbProviderServices, try to load tightly coupled Npgsql.EntityFrameworkLegacy first.

And then query NpgsqlServices.TargetProviderServices property.

We can know supported version of DbProviderServices by checking TargetProviderServices.

We provide NpgsqlServices.Instance if we share same version of EntityFramework library.
A bit more tweaking on legacy EF support

* Removed #ifdef ENTITIES, which doesn't exist anymore. We have just one Npgsql.dll.
* If the user requests legacy EF but didn't install the EntityFrameworkLegacy package/dll,
  they get an informative exception including the nested exception (is the DLL missing? corrupt?)
* If the required members inside Npgsql.EntityFramework.dll can't be found (e.g. Instance) throw
  an informative exception. This should never happen unless we mess up and release a bad DLL, but still.
* Did not understand what the TargetProviderServices property added, so removed for now
Merge pull request #110 from roji/ef6

Entity framework work for release 2.1.0