* Fixes to Pipe
- Avoid clearing out the writing head in more cases
- Allow returning a fully consumed block even if writing is in progress if it isn't writing using the current block.
- Synchronize call to Advance
* Advance can no longer be inlined
Commit migrated from https://github.com/dotnet/corefx/commit/
34765c5934c4b2f45853d323f4c87617cd2f3158