Adding warning for running from bare cmd
Update links to developer guide in error messages to new location
on the dotnet/corefx wiki.
Add System.Linq.Parallel Product and Test Code
Merge branch 'master' of https://github.com/dotnet/corefx
Cause build.cmd to set errorlevel to 1 on failed prereqs
Cause appveyor to run CI build in Dev12 developer command prompt.
Update README.md to include PLinq description.

Reviewed by @joshfree and @krwq.
Update casing of Linq -> LINQ
Disable PLinq tests failing on CI Machine
Merge pull request #175 from mellinoe/disable-plinq-tests

Disable PLinq tests failing on CI Machine
Merge pull request #174 from FiveTimesTheFun/issue-60

Update links in error messages to correct developer documentation on wiki