GitLab

Don't display the commit hash the submodule should have, but the one the
actual directory has. This allows replacing the `rust-fil-sector-builder`
with a symlink to a local version.

Old workflow:

 - Checkout submodule
 - Try to download precompiled assets
   - If downloading fails, compile the checked out submoduke

New workflow:

 - Download precompiled assets if submodule directory is empty
   - If download fails checkout the submodule
   - Compile the submodule
 - If the submodule directory is not empty, compile what is in there

The new workflow makes it easy to have a custom version of the submodule
checked out in the directory and getting everything built correctly.

* feat(porep): update API for interactive PoRep

* fix(build): grab .pc file from appropriate location

* fix(leak): point to patched sector builder

* feat(workers): configurable number worker threads

* fix(leak): point to patched sector builder

* fix(lint): use proper error formatter

* tidy

* fix(opencl): install opencl

* fix(cache): v15 cache