Remove old deprecated functions
Deprecate __FILE__ in favor of __DIR__ or __ENV__.file
Cache the environment for function definition

This speeds up compilation and reduces memory consumption. For
example, Ecto test suite consumes consistently 30% less memory
and loads 20% faster.
Move environment cache to locals tracker, which is per module
Ensure local is disabled on module definitions
Only expand __ENV__.call if it is a known function
Release v0.12.1
Start v0.12.2-dev
Do not export case and receive vars
Reenable case clause rewriting, closes #1972