Ditching __config__.py to see if it works out.

This is an experiment to see if "source mode" or "dev mode" just
uses the "right" `bezier.dll` (i.e. assuming it has been
installed) and use of `machomachomangler` would be isolated to the
creation of wheels.

.appveyor.yml

@@ -27,8 +27,8 @@ environment:
 
     # See: https://www.appveyor.com/docs/installed-software/#python
 
-    - NOX_SESSION: "win_wat"
     - NOX_SESSION: "unit-3.6-32"
+    - NOX_SESSION: "win_wat"
     - NOX_SESSION: "unit-3.6"
     - NOX_SESSION: "unit-3.7-32"
     - NOX_SESSION: "unit-3.7"
@@ -62,6 +62,8 @@ install:
       }
       $env:Path += ";$MINGW"
 
+  - ps: $env:BEZIER_DLL_PATH = "C:\projects\bezier\.nox\libbezier-debug\usr\bin"
+
   # Packaging requirements
   - python -m pip install --upgrade "pip !=20.0,!=20.0.1" setuptools
   - python -m pip install --upgrade wheel

noxfile.py

@@ -169,7 +169,11 @@ def unit(session):
     install_bezier(session, debug=True)
     # Run pytest against the unit tests.
     run_args = ["pytest"] + session.posargs + [get_path("tests", "unit")]
-    session.run(*run_args)
+    env = {}
+    bezier_dll_path = os.environ.get("BEZIER_DLL_PATH")
+    if bezier_dll_path is not None:
+        env["PATH"] = bezier_dll_path
+    session.run(*run_args, env=env)
 
 
 @nox.session(py=DEFAULT_INTERPRETER)

src/python/bezier/__init__.py

@@ -27,9 +27,6 @@
 .. autoclass:: Surface
 """
 
-# NOTE: ``__config__`` **must** be the first import because it (may)
-#       modify the search path used to locate shared libraries.
-from bezier import __config__
 from bezier._legacy import Surface
 from bezier._py_helpers import UnsupportedDegree
 from bezier.curve import Curve
@@ -41,7 +38,6 @@
 
     _HAS_SPEEDUP = True
 except ImportError as exc:  # pragma: NO COVER
-    __config__.handle_import_error(exc, "_speedup")
     _HAS_SPEEDUP = False
 # NOTE: The ``__version__`` and ``__author__`` are hard-coded here, rather
 #       than using ``pkg_resources.get_distribution("bezier").version``