Start for 0.39.0 development

Version 0.38.0

Version 0.38.0 release candidate 1

Fix 2208. Generate better error message.

This generates a better error message in the case of a type
conversion to a type unknown by the typing system.

Fixes numba#2208

Merge pull request numba#2738 from sklam/fix/whl_depends

Fix install_requires to allow pip getting pre-release version

Version 0.37.0 release candidate 1

Bug-fix release 0.36.2