RC2 Upgrade!

Tooling changes need to live in the repo now so the build doesn't FUBAR
every time we change the script.

Note: on a nuspec comparison, the following dependencies aren't there
anymore: Microsoft.CSharp, mscorlib, System, and System.Core aren't
explicitly specified in frameworkAssemblies anymore. The only one of
these I can imagine mattering is Microsoft.CSharp.

https://github.com/dotnet/corefx/issues/1612 is now closed, tests
working.

Nuget.org feed only, skip the 2 Sqlite tests until RC2+ packages with the fix are out of pre-release.

Add newer feed back **only for the tests projects**, Sqlite for example has bugs in rc1-final fixed in rc2-15948

.Net Core: remove floating versions (use stable ones on Nuget.org) and get this puppy back in action.

Also: it's 2016.

Note: no tests pass because there’s no integrated security option (or
widely available SQL server) on OS X at the moment. But the build and
test runners are up and going.

Note: these are hosed on OS X due to file handle limits, see
https://github.com/dotnet/cli/issues/809 for details.

Get building

This reverts commit 70ee9a72.

Bumping dependencies version numbers

Heh, AspNet and DNX (only) work in VS2015; DNX and DotNet (only) work in VS15; I guess we need to use DNX for now, then, as the only one that works in both.

Recreate all the xproj to reflect the current tooling - old versions break VS15; enable XDocument etc in corefx (#if block was too large)

When doing list expansions (6=>10 etc), use the last non-trivial value - do *NOT* use null, as it causes problems with "not in" clauses; add test for the same

Readme.md: update performance benchmarks tests broken link

prefer an exact-case backing-field match over a wrong-case regular field (essentially: this promotes get-only properties over regular fields)