Test revert of #4173

[dsyme]

It is possible that we should revert #4173 until we understand the issues better and to ensure stability between F# 4.1 and its update releases.

See customer-reported issue #4343

This is trialling a revert of combined commit f9893b6.

[dsyme]

@brettfo Close this since we have #4348 ? I assume you integrate dev15.6 --> master?

[dsyme]

@brettfo Is it OK if we apply this to the master branch too? I just want the core compiler logic to be in sync, so we can integrate it to Mono etc. (Mono release repo http://github.com/fsharp/fsharp is formed by integrating "master" branch here)

[brettfo]

Yes we plan on merging dev15.6 back into master, but it might be a few weeks so having this separate PR is probably a good idea.

[dsyme]

@brettfo Thanks. Merging since it was green before I opened it