This is an urgent bug-fix release, to remedy a potential deadlock error in the previous release (v0.5.0).

The only change in this release is a fix to this deadlock issue. With v0.5.0, if a compile operation was using an override version of google/protobuf/descriptor.proto, it was possible for the call to compiler.Compile to halt, only returning if the context was cancelled or times out. This is now fixed.